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Ma H, Li H, Wang J, Wang X, Wang G, Liu X. Developing Z-scheme Bi 2MoO 6@α-MnO 2 beaded core-shell heterostructure in photoelectrocatalytic treatment of organic wastewater. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2024; 367:121964. [PMID: 39067335 DOI: 10.1016/j.jenvman.2024.121964] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/24/2024] [Revised: 06/25/2024] [Accepted: 07/17/2024] [Indexed: 07/30/2024]
Abstract
Photoelectrocatalysis (PEC) oxidation technology with the combination of electrocatalysis and photocatalysis is an ideal candidate for treatment of dyeing wastewater containing multifarious intractable organic compounds with high chroma. Constructing high-quality heterojunction photoelectrodes can effectively suppress the recombination of photo-generated carriers, thereby achieving efficient removal of pollution. Herein, a beaded Bi2MoO6@α-MnO2 core-shell architecture with tunable hetero-interface was prepared by simple hydrothermal-solvothermal process. The as-synthesized Bi2MoO6@α-MnO2 had larger electrochemically active surface area, smaller charge transfer resistance and negative flat band potential, and higher separation efficiency of e-/h+ pairs than pure α-MnO2 or Bi2MoO6. It is noteworthy that the as-synthesized Bi2MoO6@α-MnO2 showed Z-scheme heterostructure as demonstrated by the free radical quenching experiments. The optimized Bi2MoO6@α-MnO2-2.5 exhibited the highest degradation rate of 88.64% in 120 min for reactive brilliant blue (KN-R) and accelerated stability with long-term(∼10000s) at the current density of 50 mA cm-2 in 1.0 mol L-1 H2SO4 solution. This study provides valuable insights into the straightforward preparation of heterogeneous electrodes, offering a promising approach for the treatment of wastewater in various industrial applications.
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Affiliation(s)
- Hongchao Ma
- School of Light Industry & Chemical Engineering, Dalian Polytechnic University, No. 1 Qinggongyuan, Ganjingzi District, Dalian, 116034, PR China
| | - Huijun Li
- School of Light Industry & Chemical Engineering, Dalian Polytechnic University, No. 1 Qinggongyuan, Ganjingzi District, Dalian, 116034, PR China
| | - Jiaxin Wang
- School of Light Industry & Chemical Engineering, Dalian Polytechnic University, No. 1 Qinggongyuan, Ganjingzi District, Dalian, 116034, PR China; Science and Technology on Aerospace Chemical Power Laboratory, Hubei Institute of Aerospace Chemotechnology, Xiangyang, 441003, PR China
| | - Xinyue Wang
- School of Textile and Material Engineering, Dalian Polytechnic University, No. 1 Qinggongyuan, Ganjingzi District, Dalian, 116034, PR China.
| | - Guowen Wang
- School of Light Industry & Chemical Engineering, Dalian Polytechnic University, No. 1 Qinggongyuan, Ganjingzi District, Dalian, 116034, PR China
| | - Xinghui Liu
- Science and Technology on Aerospace Chemical Power Laboratory, Hubei Institute of Aerospace Chemotechnology, Xiangyang, 441003, PR China.
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2
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Jeon SP, Jo JW, Nam D, Kang DW, Kim YH, Park SK. Junctionless Structure Indium-Tin Oxide Thin-Film Transistors Enabling Enhanced Mechanical and Contact Stability. ACS APPLIED MATERIALS & INTERFACES 2024; 16:38198-38207. [PMID: 38981083 DOI: 10.1021/acsami.4c03563] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/11/2024]
Abstract
In recent years, considerable attention has focused on high-performance and flexible crystalline metal oxide thin-film transistors (TFTs). However, achieving both high performance and flexibility in semiconductor devices is challenging due to the inherently conductive and brittle nature of crystalline metal oxide. In this study, we propose a facile way to overcome this limitation by employing a junctionless (JL) TFT structure via oxygen plasma treatment of the crystalline indium-tin oxide (ITO) films. The oxygen plasma treatment significantly reduced oxygen vacancies in the ITO films, contributing to the significant reduction in the carrier concentration from 4.67 × 1020 to 1.39 × 1016. Importantly, this reduction was achieved without inducing any noticeable structural changes in the ITO, enabling the successful realization of ITO JL TFTs with an adjustable threshold voltage. Furthermore, the ITO JL TFTs demonstrate good stability and reliability under various bias stress conditions, aging in the air atmosphere, and high-temperature processes. In addition, the ITO JL TFTs exhibit low light sensitivity due to the wide bandgap of ITO and further suppression of Vo defects, making them suitable for applications requiring stable performance under light exposure. To compare and analyze the flexibility of the JL structure and conventional structure with additional source/drain (S/D) junction in ITO TFTs with nonencapsulation, we utilized mechanical simulations and transmission line method (TLM). By employing the JL structure in ITO TFT through carefully optimized oxygen plasma treatment, we successfully mitigated stress concentration at the S/D-channel interface. This resulted in a JL ITO TFT that exhibited a change in contact resistance of less than 20% even after 20,000 bending cycles. Consequently, a stable and flexible ITO TFT with field-effect mobility (μFE) of 12.74 cm2/(V s) was realized, outperforming conventionally structured ITO TFTs with additional S/D junction, where the contact resistance nearly tripled.
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Affiliation(s)
- Seong-Pil Jeon
- School of Intelligent Semiconductor Engineering, Chung-Ang University, Seoul 06974, Korea
| | - Jeong-Wan Jo
- Electrical Engineering Division, Department of Engineering, University of Cambridge, Cambridge CB2 1TN, United Kingdom
| | - Dayul Nam
- School of Intelligent Semiconductor Engineering, Chung-Ang University, Seoul 06974, Korea
| | - Dong-Won Kang
- School of Intelligent Semiconductor Engineering, Chung-Ang University, Seoul 06974, Korea
| | - Yong-Hoon Kim
- School of Advanced Materials Science and Engineering and SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 16419, Korea
| | - Sung Kyu Park
- School of Intelligent Semiconductor Engineering, Chung-Ang University, Seoul 06974, Korea
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3
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Singh M, Zakria M, Pannu AS, Sonar P, Smith C, Mahasivam S, Ramanathan R, Tran K, Tawfik S, Murdoch BJ, Mayes ELH, Spencer MJS, Phillips MR, Bansal V, Ton-That C. Defect-Free, Few-Atomic-Layer Thin ZnO Nanosheets with Superior Excitonic Properties for Optoelectronic Devices. ACS NANO 2024; 18:16947-16957. [PMID: 38870404 DOI: 10.1021/acsnano.4c03098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2024]
Abstract
Two-dimensional (2D) wide bandgap materials are gaining significant interest for next-generation optoelectronic devices. However, fabricating electronic-grade 2D nanosheets from non-van der Waals (n-vdW) oxide semiconductors poses a great challenge due to their stronger interlayer coupling compared with vdW crystals. This strong coupling typically introduces defects during exfoliation, impairing the optoelectronic properties. Herein, we report the liquid-phase exfoliation of few-atomic-layer thin, defect-free, free-standing ZnO nanosheets. These micron-sized, ultrathin ZnO structures exhibit three different orientations aligned along both the polar c-plane as well as the nonpolar a- and m-planes. The superior crystalline quality of the ZnO nanosheets is validated through comprehensive characterization techniques. This result is supported by density functional theory (DFT) calculations, which reveals that the formation of oxygen vacancies is energetically less favorable in 2D ZnO and that the c-plane loses its polarity upon exfoliation. Unlike bulk ZnO, which is typically dominated by defect-induced emission, the exfoliated nanosheets exhibit a strong, ambient-stable excitonic UV emission. We further demonstrate the utility of solution processing of ZnO nanosheets by their hybrid integration with organic components to produce stable light emitting diodes (LEDs) for display applications.
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Affiliation(s)
- Mandeep Singh
- Ian Potter NanoBioSensing Facility, NanoBiotechnology Research laboratory, School of Science, RMIT University, Melbourne, VIC 3000, Australia
| | - Muhammad Zakria
- School of Mathematical and Physical Sciences, University of Technology Sydney, Ultimo, NSW 2007, Australia
| | - Amandeep Singh Pannu
- School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, Brisbane, QLD 4000, Australia
| | - Prashant Sonar
- School of Chemistry, Physics, and Mechanical Engineering, Queensland University of Technology, Brisbane, QLD 4000, Australia
| | - Christopher Smith
- School of Mathematical and Physical Sciences, University of Technology Sydney, Ultimo, NSW 2007, Australia
| | - Sanje Mahasivam
- Ian Potter NanoBioSensing Facility, NanoBiotechnology Research laboratory, School of Science, RMIT University, Melbourne, VIC 3000, Australia
| | - Rajesh Ramanathan
- Ian Potter NanoBioSensing Facility, NanoBiotechnology Research laboratory, School of Science, RMIT University, Melbourne, VIC 3000, Australia
| | - Kevin Tran
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, School of Science, RMIT University, Melbourne, VIC 3001, Australia
| | - Sherif Tawfik
- ARC Centre of Excellence in Exciton Science, School of Science, RMIT University, Melbourne, VIC 3000, Australia
| | - Billy James Murdoch
- RMIT Microscopy and Microanalysis Facility, STEM College, RMIT University, Melbourne, VIC 3001, Australia
| | | | - Michelle J S Spencer
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies, School of Science, RMIT University, Melbourne, VIC 3001, Australia
| | - Matthew R Phillips
- School of Mathematical and Physical Sciences, University of Technology Sydney, Ultimo, NSW 2007, Australia
| | - Vipul Bansal
- Ian Potter NanoBioSensing Facility, NanoBiotechnology Research laboratory, School of Science, RMIT University, Melbourne, VIC 3000, Australia
| | - Cuong Ton-That
- School of Mathematical and Physical Sciences, University of Technology Sydney, Ultimo, NSW 2007, Australia
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4
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Fang S, Huang J, Tao R, Wei Q, Ding X, Yajima S, Chen Z, Zhu W, Liu C, Li Y, Yin N, Song L, Liu Y, Shi G, Wu H, Gao Y, Wen X, Chen Q, Shen Q, Li Y, Liu Z, Li Y, Ma W. Open-Shell Diradical-Sensitized Electron Transport Layer for High-Performance Colloidal Quantum Dot Solar Cells. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2023; 35:e2212184. [PMID: 36870078 DOI: 10.1002/adma.202212184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2022] [Revised: 02/17/2023] [Indexed: 05/26/2023]
Abstract
The zinc oxide (ZnO) nanoparticles (NPs) are well-documented as an excellent electron transport layer (ETL) in optoelectronic devices. However, the intrinsic surface flaw of the ZnO NPs can easily result in serious surface recombination of carriers. Exploring effective passivation methods of ZnO NPs is essential to maximize the device's performance. Herein, a hybrid strategy is explored for the first time to improve the quality of ZnO ETL by incorporating stable organic open-shell donor-acceptor type diradicaloids. The high electron-donating feature of the diradical molecules can efficiently passivate the deep-level trap states and improve the conductivity of ZnO NP film. The unique advantage of the radical strategy is that its passivation effectiveness is highly correlated with the electron-donating ability of radical molecules, which can be precisely controlled by the rational design of molecular chemical structures. The well-passivated ZnO ETL is applied in lead sulfide (PbS) colloidal quantum dot solar cells, delivering a power conversion efficiency of 13.54%. More importantly, as a proof-of-concept study, this work will inspire the exploration of general strategies using radical molecules to construct high-efficiency solution-processed optoelectronic devices.
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Affiliation(s)
- Shiwen Fang
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
- Jiangsu Key Laboratory of Advanced Negative Carbon Technologies, Soochow University, Suzhou, Jiangsu, 215123, P. R. China
| | - Jiaxing Huang
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, 510640, P. R. China
| | - Ran Tao
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Qi Wei
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, 510640, P. R. China
| | - Xiaobo Ding
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Shota Yajima
- Faculty of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan
| | - Zhongxin Chen
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, 510640, P. R. China
| | - Weiya Zhu
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, 510640, P. R. China
| | - Cheng Liu
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Yusheng Li
- Faculty of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan
| | - Ni Yin
- i-Lab, CAS Key Laboratory of Nanophotonic Materials and Devices, Suzhou Institute of Nano-Tech and Nano-Bionics, Suzhou, 215123, China
| | - Leliang Song
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Yang Liu
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Guozheng Shi
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Hao Wu
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Yiyuan Gao
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Xin Wen
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Qi Chen
- i-Lab, CAS Key Laboratory of Nanophotonic Materials and Devices, Suzhou Institute of Nano-Tech and Nano-Bionics, Suzhou, 215123, China
| | - Qing Shen
- Faculty of Informatics and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan
| | - Youyong Li
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
| | - Zeke Liu
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
- Jiangsu Key Laboratory of Advanced Negative Carbon Technologies, Soochow University, Suzhou, Jiangsu, 215123, P. R. China
| | - Yuan Li
- Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, 510640, P. R. China
| | - Wanli Ma
- Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Joint International Research Laboratory of Carbon-Based Functional Materials and Devices, Soochow University, 199 Ren'ai Road, Suzhou, Jiangsu, 215123, China
- Jiangsu Key Laboratory of Advanced Negative Carbon Technologies, Soochow University, Suzhou, Jiangsu, 215123, P. R. China
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5
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Hussain S, Okai Amu-Darko JN, Wang M, Alothman AA, Ouladsmane M, Aldossari SA, Khan MS, Qiao G, Liu G. CuO-decorated MOF derived ZnO polyhedral nanostructures for exceptional H 2S gas detection. CHEMOSPHERE 2023; 317:137827. [PMID: 36646181 DOI: 10.1016/j.chemosphere.2023.137827] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Revised: 12/07/2022] [Accepted: 01/10/2023] [Indexed: 06/17/2023]
Abstract
Considering that H2S is a hazardous gas that poses a significant risk to people's lives, research into H2S gas sensors has garnered a lot of interest. This work reports a CuO/ZnO multifaceted nanostructures(NS) created by heat treating Cu2+/ZIF-8 impregnation precursors, and their microstructure and gas sensing characteristics were examined using various characterization techniques (XRD, XPS, SEM, TEM, and BET). The as-prepared hollow CuO/ZnO multifunctional nanostructures had a high gas response value (425@50 ppm H2S gas), quick response and recovery times (57/191s @20 ppm), a low limit of detection (1.6@500 ppb H2S), good humidity resistance and highly selective towards H2S gas. The hollow CuO/ZnO multifaceted nanostructures possessed enhanced gas sensing capabilities which may be related to their porous hollow nanostructures, the manufactured p-CuO/n-ZnO heterojunctions, and the spillover effect between CuO and H2S.
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Affiliation(s)
- Shahid Hussain
- School of Materials Science and Engineering, Jiangsu University, Zhenjiang, 212013, China.
| | | | - Mingsong Wang
- School of Materials Science and Engineering, Jiangsu University, Zhenjiang, 212013, China
| | - Asma A Alothman
- Department of Chemistry, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia
| | - Mohamed Ouladsmane
- Department of Chemistry, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia
| | - Samar A Aldossari
- Department of Chemistry, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia
| | - Muhammad Shahzeb Khan
- Department of Chemistry and Technology of Functional Materials, Gdansk University of Technology, Faculty of Chemistry, Narutowicza 11/12, 80-233, Gdansk, Poland
| | - Guanjun Qiao
- School of Materials Science and Engineering, Jiangsu University, Zhenjiang, 212013, China
| | - Guiwu Liu
- School of Materials Science and Engineering, Jiangsu University, Zhenjiang, 212013, China.
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6
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Abstract
Due to the untiring efforts of scientists and researchers on oxide semiconductor materials, processes, and devices, the applications for oxide-based thin film transistors (TFTs) have been researched and promoted on a large scale. With the advantages of relatively high carrier mobility, low off-current, good process compatibility, optical transparency, low cost, and especially flexibility, oxide-based TFTs have already been adapted for not only displays (e.g., liquid crystal display (LCD), organic light emitting diode (OLED), micro-light-emitting diode (Micro-LED), virtual reality/augmented reality (VR/AR) and electronic paper displays (EPD)) but also large-area electronics, analog circuits, and digital circuits. Furthermore, as the requirement of TFT technology increases, low temperature poly-silicon and oxide (LTPO) TFTs, which combine p-type LTPS and n-type oxide TFT on the same substrate, have drawn further interest for realizing the hybrid complementary metal oxide semiconductor (CMOS) circuit. This invited review provides the current progress on applications of oxide-based TFTs. Typical device configurations of TFTs are first described. Then, the strategies to apply oxide-based TFTs for improving the display quality with different compensation technologies and obtaining higher performance integrated circuits are highlighted. Finally, an outlook for the future development of oxide-based TFTs is given.
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7
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Improved Negative Bias Stress Stability of Sol–Gel-Processed Li-Doped SnO2 Thin-Film Transistors. ELECTRONICS 2021. [DOI: 10.3390/electronics10141629] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In this study, sol–gel-processed Li-doped SnO2-based thin-film transistors (TFTs) were fabricated on SiO2/p+ Si substrates. The influence of Li dopant (wt%) on the structural, chemical, optical, and electrical characteristics was investigated. By adding 0.5 wt% Li dopant, the oxygen vacancy formation process was successfully suppressed. Its smaller ionic size and strong bonding strength made it possible for Li to work as an oxygen vacancy suppressor. The fabricated TFTs consisting of 0.5 wt% Li-doped SnO2 semiconductor films delivered the field-effect mobility in a 2.0 cm2/Vs saturation regime and Ion/Ioff value of 1 × 108 and showed enhancement mode operation. The decreased oxygen vacancy inside SnO2 TFTs with 0.5 wt% Li dopant improved the negative bias stability of TFTs.
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8
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Martinez EY, Zhu K, Li CW. Influence of the Defect Stability on n-Type Conductivity in Electron-Doped α- and β-Co(OH) 2 Nanosheets. Inorg Chem 2021; 60:6950-6956. [PMID: 33835781 DOI: 10.1021/acs.inorgchem.1c00455] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Electronic doping of transition-metal oxides (TMOs) is typically accomplished through the synthesis of nonstoichiometric oxide compositions and the subsequent ionization of intrinsic lattice defects. As a result, ambipolar doping of wide-band-gap TMOs is difficult to achieve because the formation energies and stabilities of vacancy and interstitial defects vary widely as a function of the oxide composition and crystal structure. The facile formation of lattice defects for one carrier type is frequently paired with the high-energy and unstable generation of defects required for the opposite carrier polarity. Previous work from our group showed that the brucite (β-phase) layered metal hydroxides of Co and Ni, intrinsically p-type materials in their anhydrous three-dimensional forms, could be n-doped using a strong chemical reductant. In this work, we extend the electron-doping study to the α polymorph of Co(OH)2 and elucidate the defects responsible for n-type doping in these two-dimensional materials. Through structural and electronic comparisons between the α, β, and rock-salt structures within the cobalt (hydr)oxide family of materials, we show that both layered structures exhibit facile formation of anion vacancies, the necessary defect for n-type doping, that are not accessible in the cubic CoO structure. However, the brucite polymorph is much more stable to reductive decomposition in the presence of doped electrons because of its tighter layer-to-layer stacking and octahedral coordination geometry, which results in a maximum conductivity of 10-4 S/cm, 2 orders of magnitude higher than the maximum value attainable on the α-Co(OH)2 structure.
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Affiliation(s)
- Eve Y Martinez
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Kuixin Zhu
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
| | - Christina W Li
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States
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9
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Role of the paramagnetic donor-like defects in the high n-type conductivity of the hydrogenated ZnO microparticles. Sci Rep 2020; 10:17347. [PMID: 33060736 PMCID: PMC7567118 DOI: 10.1038/s41598-020-74449-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Accepted: 10/01/2020] [Indexed: 11/16/2022] Open
Abstract
The magnetic and electronic properties of the hydrogenated highly conductive zinc oxide (ZnO) microparticles were investigated by electron paramagnetic resonance (EPR) and contactless microwave (MW) conductivity techniques in the wide temperature range. The EPR spectra simulation allowed us to resolve four overlapping EPR signals in ZnO microparticles. The Lorentzian EPR line with isotropic g-factor 1.9623(5) was related to the singly ionized oxygen vacancy. Another Lorentzian line with g|| = 1.9581(5), g⊥ = 1.9562(5) was attributed to the zinc interstitial shallow donor center, while EPR signal with g|| = 1.9567(5), g⊥ = 1.9556(5) and Gaussian lineshape was assigned to the hydrogen interstitial shallow effective-mass-like donor. The EPR signal with g|| = 1.9538(5), g⊥ = 1.9556(5) and Lorentzian lineshape was tentatively attributed to the shallow donor center. The charge transport properties in ZnO microparticles have been investigated by the contactless MW conductivity technique at T = 5–296 K. Two conduction mechanisms, including ionization of electrons from the shallow donors to the conduction band and hopping conduction process, have been distinguished. The hopping conduction process follows Mott’s variable-range hopping T−1/4 law at T = 10–100 K. The evaluated values of the average hopping distance (15.86 Å), and hopping energy (1.822 meV at 40 K) enable us to estimate the donor concentration in the investigated ZnO microparticles as ~ 1018 cm−3.
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10
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Blake JC, Nieto-Pescador J, Li Z, Gundlach L. Femtosecond Luminescence Imaging for Single Nanoparticle Characterization. J Phys Chem A 2020; 124:4583-4593. [PMID: 32427477 DOI: 10.1021/acs.jpca.0c01775] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Defects naturally abound in semiconductor crystal structures and their presence either debilitates or improves device functionality. The increasing trend to strategically implant or remove specific defects to tailor the properties in materials via defect engineering has made it imperative to not only quantify these defects in nanostructures but to do so via efficient contactless techniques. Here we report the use of an ultrafast Kerr-gated microscope system to quantify the defect density at different locations on a single nanowire. By measuring the evolution of nonlinear luminescence dynamics from a nanowire, we are able to extract the individual nonradiative recombination constants and obtain the defect density at locations along the nanowire length. This new method promises fast, reliable, and contactless characterization of single nanoparticles.
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Affiliation(s)
- Jolie C Blake
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States
| | - Jesus Nieto-Pescador
- Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, United States
| | - Zhengxin Li
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States
| | - Lars Gundlach
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States.,Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, United States
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11
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Effect of Mg Doping on the Electrical Performance of a Sol-Gel-Processed SnO2 Thin-Film Transistor. ELECTRONICS 2020. [DOI: 10.3390/electronics9030523] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Sol-gel-processed Mg-doped SnO2 thin-film transistors (TFTs) were successfully fabricated. The effect of Mg concentration on the structural, chemical, and optical properties of thin films and the corresponding TFT devices was investigated. The results indicated that an optimal Mg concentration yielded an improved negative bias stability and increased optical band gap, resulting in transparent devices. Furthermore, the optimal device performance was obtained with 0.5 wt% Mg. The fabricated 0.5 wt% Mg-doped SnO2 TFT was characterized by a field effect mobility, a subthreshold swing, and Ion/Ioff ratio of 4.23 cm2/Vs, 1.37 V/decade, and ~1 × 107, respectively. The added Mg suppressed oxygen-vacancy formation, thereby improving the bias stability. This work may pave the way for the development of alkaline-earth-metal-doped SnO2-based thin-film devices.
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12
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Sarkar A, Chakrabarti M, Sanyal D, Gogurla N, Kumar P, Brusa RS, Hugenschmidt C. Depth resolved defect characterization of energetic ion irradiated ZnO by positron annihilation techniques and photoluminescence. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:085703. [PMID: 31469094 DOI: 10.1088/1361-648x/ab3f74] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Depth resolved positron annihilation spectroscopy (PAS) has been employed to characterize the 1.2 MeV Ar and 800 keV O ion beam induced defects in ZnO. The first extraordinary result was the observation of defects in ion beam irradiated ZnO beyond the maximum penetration depth of the respective ions. The positron annihilation results revealed the formation of vacancy clusters consisting of both VZn and VO in ZnO which are saturated at a threshold radiation dose (defined as nuclear energy loss, Sn × fluence). From the photoluminescence (PL) spectra it has been observed that the PL intensity at the band edge degraded with the increase of open volume defects in ZnO. The evolution of the 2.4 eV PL, which is linked with the oxygen vacancies, is more significant due to Ar irradiation than the oxygen irradiation.
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Affiliation(s)
- A Sarkar
- Department of Physics, Bangabasi Morning College, 19 Rajkumar Chakraborty Sarani, Kolkata 700 009, India
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13
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Abstract
Y-doped SnO2 thin film transistors were successfully fabricated by means of sol-gel process. The effect of Y concentration on the structural, chemical, and electrical properties of sol-gel-processed SnO2 films was investigated via GIXRD, SPM, and XPS; the corresponding electrical transport properties of the film were also evaluated. The dopant, Y, can successfully control the free carrier concentration by suppressing the formation of oxygen vacancy inside SnO2 semiconductors due to its lower electronegativity and SEP. With an increase of Ywt%, it was observed that the crystallinity and oxygen vacancy concentration decreased, and the operation mode of SnO2 thin film transistor changed from accumulation (normally on) to enhancement mode (normally off) with a positive Vth shift.
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14
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Effect of Annealing Ambient on SnO2 Thin Film Transistors Fabricated via An Ethanol-based Sol-gel Route. ELECTRONICS 2019. [DOI: 10.3390/electronics8090955] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The effect of annealing ambient on SnO2 thin-film transistors (TFTs) fabricated via an ethanol-based sol-gel route was investigated. The annealing ambient has a significant effect on the structural characteristics and chemical composition and, in turn, the device performance. Although the crystalline-grain size of the SnO2 films annealed in air was the smallest, this size yielded the highest field-effect mobility. Compared with the minimization of boundary scattering via crystalline-size increase, augmentation of the free carrier concentration played a more critical role in the realization of high-performance devices. The fabricated SnO2 TFTs delivered a field-effect mobility, subthreshold swing, and on/off current ratio of 10.87 cm2/Vs, 0.87 V/decade, and 107, respectively.
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15
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Lee J, Schell W, Zhu X, Kioupakis E, Lu WD. Charge Transition of Oxygen Vacancies during Resistive Switching in Oxide-Based RRAM. ACS APPLIED MATERIALS & INTERFACES 2019; 11:11579-11586. [PMID: 30816044 DOI: 10.1021/acsami.8b18386] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Resistive random-access memory (RRAM) devices have attracted broad interest as promising building blocks for high-density nonvolatile memory and neuromorphic computing applications. Atomic level thermodynamic and kinetic descriptions of resistive switching (RS) processes are essential for continued device design and optimization but are relatively lacking for oxide-based RRAMs. It is generally accepted that RS occurs due to the redistribution of charged oxygen vacancies driven by an external electric field. However, this assumption contradicts the experimentally observed stable filaments, where the high vacancy concentration should lead to a strong Coulomb repulsion and filament instability. In this work, through predictive atomistic calculations in combination with experimental measurements, we attempt to understand the interactions between oxygen vacancies and the microscopic processes that are required for stable RS in a Ta2O5-based RRAM. We propose a model based on a series of charge transition processes that explains the drift and aggregation of vacancies during RS. The model was validated by experimental measurements where illuminated devices exhibit accelerated RS behaviors during SET and RESET. The activation energies of ion migration and charge transition were further experimentally determined through a transient current measurement, consistent with the modeling results. Our results help provide comprehensive understanding on the internal dynamics of RS and will benefit device optimization and applications.
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16
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Research Progress on Flexible Oxide-Based Thin Film Transistors. APPLIED SCIENCES-BASEL 2019. [DOI: 10.3390/app9040773] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Oxide semiconductors have drawn much attention in recent years due to their outstanding electrical performance, such as relatively high carrier mobility, good uniformity, low process temperature, optical transparency, low cost and especially flexibility. Flexible oxide-based thin film transistors (TFTs) are one of the hottest research topics for next-generation displays, radiofrequency identification (RFID) tags, sensors, and integrated circuits in the wearable field. The carrier transport mechanism of oxide semiconductor materials and typical device configurations of TFTs are firstly described in this invited review. Then, we describe the research progress on flexible oxide-based TFTs, including representative TFTs fabricated on different kinds of flexible substrates, the mechanical stress effect on TFTs and optimized methods to reduce this effect. Finally, an outlook for the future development of oxide-based TFTs is given.
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17
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Lee YJ, Kim HH, Lee YJ, Kim JH, Choi HJ, Choi WK. Electron transport phenomena at the interface of Al electrode and heavily doped degenerate ZnO nanoparticles in quantum dot light emitting diode. NANOTECHNOLOGY 2019; 30:035207. [PMID: 30452390 DOI: 10.1088/1361-6528/aaed98] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
ZnO nanoparticles (NPs) of 4-5 nm, widely adopted as an electron transport layer (ETL) in quantum dot light emitting diodes (QD-LEDs), were synthesized using the solution-precipitation process. It is notable that synthesized ZnO NPs are highly degenerate intrinsic semiconductors and their donor concentration can be increased up to N D = 6.9 × 1021 cm-3 by annealing at 140 °C in air. An optical bandgap increase of as large as 0.16-0.33 eV by degeneracy is explained well by the Burstein-Moss shift. In order to investigate the influence of intrinsic defects of ZnO NP ETLs on the performance of QD-LED devices without a combined annealing temperature between ZnO NP ETLs and the emissive QD layer, pre-annealed ZnO NPs at 60 °C, 90 °C, 140 °C, and 180 °C were spin-coated on the annealed QD layer without further post-annealing. As the annealing temperature increases from 60 °C to 180 °C, the defect density related to oxygen vacancy (V O) in ZnO NPs is reduced from 34.4% to 17.8%, whereas the defect density of interstitial Zn (Zni) is increased. Increased Zni reduces the width (W) of the depletion region from 0.21 to 0.12 nm and lowers the Schottky barrier (ФB) between ZnO NPs and the Al electrode from 1.19 to 0.98 eV. We reveal for the first time that carrier conduction between ZnO NP ETLs and the Al electrode is largely affected by the concentration of Zni above the conduction band minimum, and effectively described by space charge limited current and trap charge limited current models.
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Affiliation(s)
- Yeon Ju Lee
- Center for Opto-Electronic Materials and Devices, Korea Institute of Science and Technology (KIST), Seoul, 02792, Republic of Korea. Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea
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18
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Tzitzeklis CA, Gupta JK, Dyer MS, Manning TD, Pitcher MJ, Niu HJ, Savvin S, Alaria J, Darling GR, Claridge JB, Rosseinsky MJ. Computational Prediction and Experimental Realization of p-Type Carriers in the Wide-Band-Gap Oxide SrZn 1- xLi xO 2. Inorg Chem 2018; 57:11874-11883. [PMID: 30198714 DOI: 10.1021/acs.inorgchem.8b00697] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
It is challenging to achieve p-type doping of zinc oxides (ZnO), which are of interest as transparent conductors in optoelectronics. A ZnO-related ternary compound, SrZnO2, was investigated as a potential host for p-type conductivity. First-principles investigations were used to select from a range of candidate dopants the substitution of Li+ for Zn2+ as a stable, potentially p-type, doping mechanism in SrZnO2. Subsequently, single-phase bulk samples of a new p-type-doped oxide, SrZn1- xLi xO2 (0 < x < 0.06), were prepared. The structural, compositional, and physical properties of both the parent SrZnO2 and SrZn1- xLi xO2 were experimentally verified. The band gap of SrZnO2 was calculated using HSE06 at 3.80 eV and experimentally measured at 4.27 eV, which confirmed the optical transparency of the material. Powder X-ray diffraction and inductively coupled plasma analysis were combined to show that single-phase ceramic samples can be accessed in the compositional range x < 0.06. A positive Seebeck coefficient of 353(4) μV K-1 for SrZn1- xLi xO2, where x = 0.021, confirmed that the compound is a p-type conductor, which is consistent with the pO2 dependence of the electrical conductivity observed in all SrZn1- xLi xO2 samples. The conductivity of SrZn1- xLi xO2 is up to 15 times greater than that of undoped SrZnO2 (for x = 0.028 σ = 2.53 μS cm-1 at 600 °C and 1 atm of O2).
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Affiliation(s)
- Christos A Tzitzeklis
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - Jyoti K Gupta
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - Matthew S Dyer
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - Troy D Manning
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - Michael J Pitcher
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - Hongjun J Niu
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - Stanislav Savvin
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - Jonathan Alaria
- Department of Physics , University of Liverpool , Liverpool , L69 7ZE , U.K
| | - George R Darling
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - John B Claridge
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
| | - Matthew J Rosseinsky
- Department of Chemistry, Materials Innovation Factory , University of Liverpool , 51 Oxford Street , Liverpool , L7 3NY , U.K
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19
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Kegel J, Zubialevich VZ, Schmidt M, Povey IM, Pemble ME. Effect of Surface and Defect Chemistry on the Photocatalytic Properties of Intentionally Defect-Rich ZnO Nanorod Arrays. ACS APPLIED MATERIALS & INTERFACES 2018; 10:17994-18004. [PMID: 29737166 DOI: 10.1021/acsami.8b05130] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Due to the abundance of intrinsic defects in zinc oxide (ZnO), the material properties are often governed by same. Knowledge of the defect chemistry has proven to be highly important, especially in terms of the photocatalytic degradation of pollutants. Given the fact that defect-free materials or structures exhibiting only one type of defect are extremely difficult to produce, it is necessary to evaluate what influence various defects may have when present together in the material. In this study, intentionally defect-rich ZnO nanorod (NR) arrays are grown using a simple low-temperature solution-based growth technique. Upon changing the defect chemistry using rapid thermal annealing (RTA) the material properties are carefully assessed and correlated to the resulting photocatalytic properties. Special focus is put on the investigation of these properties for samples showing strong orange photoluminescence (PL). It is shown that intense orange emitting NR arrays exhibit improved dye-degradation rates under UV-light irradiation. Furthermore, strong dye-adsorption has been observed for some samples. This behavior is found to stem from a graphitic surface structure (e.g., shell) formed during RTA in vacuum. Since orange-luminescent samples also exhibit an enhancement of the dye adsorption a possible interplay and synergy of these two defects is elucidated. Additionally, evidence is presented suggesting that in annealed ZnO NRs structural defects may be responsible for the often observed PL emission at 3.31 eV. However, a clear correlation with the photocatalytic properties could not be established for these defects. Building on the specific findings presented here, this study also presents some more general guidelines which, it is suggested, should be employed when assessing the photocatalytic properties of defect-rich ZnO.
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Affiliation(s)
- Jan Kegel
- Tyndall National Institute, University College Cork , Lee Maltings , Cork , Ireland
| | - Vitaly Z Zubialevich
- Tyndall National Institute, University College Cork , Lee Maltings , Cork , Ireland
| | - Michael Schmidt
- Tyndall National Institute, University College Cork , Lee Maltings , Cork , Ireland
| | - Ian M Povey
- Tyndall National Institute, University College Cork , Lee Maltings , Cork , Ireland
| | - Martyn E Pemble
- Tyndall National Institute, University College Cork , Lee Maltings , Cork , Ireland
- Department of Chemistry , University College Cork , Cork , Ireland
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20
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Electrochemical photocurrent enhancement in a ZnO-perovskite heterojunction using piezoelectric effect. Electrochim Acta 2018. [DOI: 10.1016/j.electacta.2018.02.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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21
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El-Taib Heakal F, Abd-Ellatif WR, Tantawy NS, Taha AA. Characterization of electrodeposited undoped and doped thin ZnO passive films on zinc metal in alkaline HCO3−/CO32− buffer solution. RSC Adv 2018; 8:39321-39333. [PMID: 35558032 PMCID: PMC9091022 DOI: 10.1039/c8ra06899b] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Accepted: 11/19/2018] [Indexed: 11/22/2022] Open
Abstract
Electrochemical characterization of anodically grown thin ZnO films on pure zinc metal was studied in pH 9.2 bicarbonate/carbonate buffer solution. The different undoped passive films were formed potentiostatically in pH 9.2 borate buffer solution at processing anodic voltage (Va) of −1.04, −1.02, −1.0 and −0.99 V (vs. Ag/AgCl). While, various doped ZnO films were fabricated by anodizing the metal at a fixed potential of −1.00 V in the same borate buffer solution containing different amounts of LiCl or InCl3. The electrochemical and semiconducting properties of all formed films were investigated using chronoamperometric measurements, EIS and Mott–Schottky analysis supported by scanning electron microscopy. The impedance results showed a direct correlation between Va and the value of either total resistance (Rf) of undoped passive film or its thickness (δf). It is evident that anodization can afford better conditions for forming thicker compact passive films with more advanced barrier properties. On the other hand, Rf decreases with increasing Li-doping level in the oxide film, and increases in case of In-doping. Interestingly, Rf values of the doped films are always lower when compared to its value for the undoped film grown at −1.00 V, likely due to possible change in the film microstructure upon doping. For both undoped and doped ZnO films, Mott–Schottky plots reveals unintentional n-type conductivity with high electron density. Moreover, with increasing dopant level in ZnO host materials, Mott–Schottky analysis revealed a parallel correlation between charge carrier donor concentration (ND) and the passive film thickness (δf), where the trend of their values are to decrease for Li+-doped and to increase for In3+-doped films. The trend of charge carrier density (ND) and film thickness (δf) dependence on the parameter is indicated on each arrow for undoped, Li-doped, and In-doped ZnO semiconductor materials.![]()
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Affiliation(s)
- F. El-Taib Heakal
- Chemistry Department
- Faculty of Science
- Cairo University
- Giza 12613
- Egypt
| | - W. R. Abd-Ellatif
- Faculty of Women for Arts
- Science and Education
- Ain Shams University
- Cairo 11566
- Egypt
| | - N. S. Tantawy
- Faculty of Women for Arts
- Science and Education
- Ain Shams University
- Cairo 11566
- Egypt
| | - A. A. Taha
- Faculty of Women for Arts
- Science and Education
- Ain Shams University
- Cairo 11566
- Egypt
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22
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Ding X, Qin C, Song J, Zhang J, Jiang X, Zhang Z. The Influence of Hafnium Doping on Density of States in Zinc Oxide Thin-Film Transistors Deposited via Atomic Layer Deposition. NANOSCALE RESEARCH LETTERS 2017; 12:63. [PMID: 28116611 PMCID: PMC5256629 DOI: 10.1186/s11671-017-1852-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2016] [Accepted: 01/17/2017] [Indexed: 05/27/2023]
Abstract
Thin-film transistors (TFTs) with atomic layer deposition (ALD) HfZnO (HZO) as channel layer and Al2O3 as gate insulator were successfully fabricated. Compared with ZnO-TFT, the stability of HZO-TFT was obviously improved as Hf doping can suppress the generation of oxygen related defects. The transfer characteristics of TFTs at different temperatures were also investigated, and temperature stability enhancement was observed for the TFT with Hf doping. The density of states (DOS) was calculated based on the experimentally obtained E a, which can explain the experimental observation. A high-field effect mobility of 9.4 cm2/Vs, a suitable turn-on voltage of 0.26 V, a high on/off ratio of over 107 and a steep sub-threshold swing of 0.3 V/decade were obtained in HZO-TFT. The results showed that temperature stability enhancement in HfZnO thin-film transistors are attributed to the smaller DOS.
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Affiliation(s)
- Xingwei Ding
- Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai University, 149 Yanchang Road, Jingan District, Shanghai, 200070, People's Republic of China
- School of Mechatronics and Automation, Shanghai University, Shanghai, 200072, China
| | - Cunping Qin
- School of Mechatronics and Automation, Shanghai University, Shanghai, 200072, China
| | - Jiantao Song
- Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai University, 149 Yanchang Road, Jingan District, Shanghai, 200070, People's Republic of China
| | - Jianhua Zhang
- Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai University, 149 Yanchang Road, Jingan District, Shanghai, 200070, People's Republic of China.
- School of Mechatronics and Automation, Shanghai University, Shanghai, 200072, China.
| | - Xueyin Jiang
- Department of Materials Science, Shanghai University, Shanghai, 200072, China
| | - Zhilin Zhang
- Key Laboratory of Advanced Display and System Application, Ministry of Education, Shanghai University, 149 Yanchang Road, Jingan District, Shanghai, 200070, People's Republic of China
- Department of Materials Science, Shanghai University, Shanghai, 200072, China
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Park J, Jeong HJ, Lee HM, Nahm HH, Park JS. The resonant interaction between anions or vacancies in ZnON semiconductors and their effects on thin film device properties. Sci Rep 2017; 7:2111. [PMID: 28522801 PMCID: PMC5437099 DOI: 10.1038/s41598-017-02336-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Accepted: 04/11/2017] [Indexed: 11/23/2022] Open
Abstract
Zinc oxynitride (ZnON) semiconductors are suitable for high performance thin-film transistors (TFTs) with excellent device stability under negative bias illumination stress (NBIS). The present work provides a first approach on the optimization of electrical performance and stability of the TFTs via studying the resonant interaction between anions or vacancies in ZnON. It is found that the incorporation of nitrogen increases the concentration of nitrogen vacancies (VN+s), which generate larger concentrations of free electrons with increased mobility. However, a critical amount of nitrogen exists, above which electrically inactive divacancy (VN-VN)0 forms, thus reducing the number of carriers and their mobility. The presence of nitrogen anions also reduces the relative content of oxygen anions, therefore diminishing the probability of forming O-O dimers (peroxides). The latter is well known to accelerate device degradation under NBIS. Calculations indicate that a balance between device performance and NBIS stability may be achieved by optimizing the nitrogen to oxygen anion ratio. Experimental results confirm that the degradation of the TFTs with respect to NBIS becomes less severe as the nitrogen content in the film increases, while the device performance reaches an intermediate peak, with field effect mobility exceeding 50 cm2/Vs.
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Affiliation(s)
- Jozeph Park
- Department of Materials Science and Engineering, KAIST, Daejeon, 34141, Republic of Korea.,R&D Center, Samsung Display, Yongin, 17113, Republic of Korea
| | - Hyun-Jun Jeong
- Department of Materials Science and Engineering, Hanyang University, Seoul, 04763, Republic of Korea
| | - Hyun-Mo Lee
- Department of Materials Science and Engineering, Hanyang University, Seoul, 04763, Republic of Korea
| | - Ho-Hyun Nahm
- Center for Correlated Electron Systems, Institute for Basic Science (IBS), Seoul, 08826, Republic of Korea. .,Department of Physics and Astronomy, Seoul National University (SNU), Seoul, 08826, Republic of Korea. .,Graduate School of Nanoscience and Technology, Korea Advanced Institute of Science and Technology, Daejeon, Republic of Korea.
| | - Jin-Seong Park
- Department of Materials Science and Engineering, Hanyang University, Seoul, 04763, Republic of Korea.
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24
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Kegel J, Laffir F, Povey IM, Pemble ME. Defect-promoted photo-electrochemical performance enhancement of orange-luminescent ZnO nanorod-arrays. Phys Chem Chem Phys 2017; 19:12255-12268. [DOI: 10.1039/c7cp01606a] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Defect engineering in ZnO: origin of strong orange-luminescent defects in solution-grown nanorod-arrays and their enhanced photo-electrochemical performance.
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Affiliation(s)
- Jan Kegel
- Tyndall National Institute, University College Cork, Lee Maltings
- Cork
- Ireland
| | | | - Ian M. Povey
- Tyndall National Institute, University College Cork, Lee Maltings
- Cork
- Ireland
| | - Martyn E. Pemble
- Tyndall National Institute, University College Cork, Lee Maltings
- Cork
- Ireland
- Department of Chemistry
- University College Cork
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25
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Sheng J, Lee HJ, Oh S, Park JS. Flexible and High-Performance Amorphous Indium Zinc Oxide Thin-Film Transistor Using Low-Temperature Atomic Layer Deposition. ACS APPLIED MATERIALS & INTERFACES 2016; 8:33821-33828. [PMID: 27960372 DOI: 10.1021/acsami.6b11774] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Amorphous indium zinc oxide (IZO) thin films were deposited at different temperatures, by atomic layer deposition (ALD) using [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (INCA-1) as the indium precursor, diethlzinc (DEZ) as the zinc precursor, and hydrogen peroxide (H2O2) as the reactant. The ALD process of IZO deposition was carried by repeated supercycles, including one cycle of indium oxide (In2O3) and one cycle of zinc oxide (ZnO). The IZO growth rate deviates from the sum of the respective In2O3 and ZnO growth rates at ALD growth temperatures of 150, 175, and 200 °C. We propose growth temperature-dependent surface reactions during the In2O3 cycle that correspond with the growth-rate results. Thin-film transistors (TFTs) were fabricated with the ALD-grown IZO thin films as the active layer. The amorphous IZO TFTs exhibited high mobility of 42.1 cm2 V-1 s-1 and good positive bias temperature stress stability. Finally, flexible IZO TFT was successfully fabricated on a polyimide substrate without performance degradation, showing the great potential of ALD-grown TFTs for flexible display applications.
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Affiliation(s)
- Jiazhen Sheng
- Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Republic of Korea
| | - Hwan-Jae Lee
- Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Republic of Korea
| | - Saeroonter Oh
- Division of Electrical Engineering, Hanyang University , Ansan, Gyeonggi-do 15588, Republic of Korea
| | - Jin-Seong Park
- Division of Materials Science and Engineering, Hanyang University , Seoul 04763, Republic of Korea
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Sheng J, Park J, Choi DW, Lim J, Park JS. A Study on the Electrical Properties of Atomic Layer Deposition Grown InO x on Flexible Substrates with Respect to N 2O Plasma Treatment and the Associated Thin-Film Transistor Behavior under Repetitive Mechanical Stress. ACS APPLIED MATERIALS & INTERFACES 2016; 8:31136-31143. [PMID: 27798828 DOI: 10.1021/acsami.6b11815] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Indium oxide (InOx) films were deposited at low processing temperature (150 °C) by atomic layer deposition (ALD) using [1,1,1-trimethyl-N-(trimethylsilyl)silanaminato]indium (InCA-1) as the metal precursor and hydrogen peroxide (H2O2) as the oxidant. As-deposited InOx exhibits a metallic conductor-like behavior owing to a relatively high free-carrier concentration. In order to control the electron density in InOx layers, N2O plasma treatment was carried out on the film surface. The exposure time to N2O plasma was varied (600-2400 s) to evaluate its effect on the electrical properties of InOx. In this regard, thin-film transistors (TFTs) utilizing this material as the active layer were fabricated on polyimide substrates, and transfer curves were measured. As the plasma treatment time increases, the TFTs exhibit a transition from metal-like conductor to a high-performance switching device. This clearly demonstrates that the N2O plasma has an effect of diminishing the carrier concentration in InOx. The combination of low-temperature ALD and N2O plasma process offers the possibility to achieve high-performance devices on polymer substrates. The electrical properties of InOx TFTs were further examined with respect to various radii of curvature and repetitive bending of the substrate. Not only does prolonged cyclic mechanical stress affect the device properties, but the bending direction is also found to be influential. Understanding such behavior of flexible InOx TFTs is anticipated to provide effective ways to design and achieve reliable electronic applications with various form factors.
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Affiliation(s)
- Jiazhen Sheng
- Division of Materials Science and Engineering, Hanyang University , 222 Wangsimni-ro Seongdong-gu, Seoul, 04763, Republic of Korea
| | - Jozeph Park
- Department of Materials Science and Engineering, KAIST , 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Dong-Won Choi
- Division of Materials Science and Engineering, Hanyang University , 222 Wangsimni-ro Seongdong-gu, Seoul, 04763, Republic of Korea
| | - Junhyung Lim
- Display Research and Development Center, Samsung Display Company, Limited , Yongin 446-711, Republic of Korea
| | - Jin-Seong Park
- Division of Materials Science and Engineering, Hanyang University , 222 Wangsimni-ro Seongdong-gu, Seoul, 04763, Republic of Korea
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Siol S, Hellmann JC, Tilley SD, Graetzel M, Morasch J, Deuermeier J, Jaegermann W, Klein A. Band Alignment Engineering at Cu2O/ZnO Heterointerfaces. ACS APPLIED MATERIALS & INTERFACES 2016; 8:21824-31. [PMID: 27452037 DOI: 10.1021/acsami.6b07325] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Energy band alignments at heterointerfaces play a crucial role in defining the functionality of semiconductor devices, yet the search for material combinations with suitable band alignments remains a challenge for numerous applications. In this work, we demonstrate how changes in deposition conditions can dramatically influence the functional properties of an interface, even within the same material system. The energy band alignment at the heterointerface between Cu2O and ZnO was studied using photoelectron spectroscopy with stepwise deposition of ZnO onto Cu2O and vice versa. A large variation of energy band alignment depending on the deposition conditions of the substrate and the film is observed, with valence band offsets in the range ΔEVB = 1.45-2.7 eV. The variation of band alignment is accompanied by the occurrence or absence of band bending in either material. It can therefore be ascribed to a pinning of the Fermi level in ZnO and Cu2O, which can be traced back to oxygen vacancies in ZnO and to metallic precipitates in Cu2O. The intrinsic valence band offset for the interface, which is not modified by Fermi level pinning, is derived as ΔEVB ≈ 1.5 eV, being favorable for solar cell applications.
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Affiliation(s)
- Sebastian Siol
- Technische Universität Darmstadt , Institute of Materials Science, Surface Science Division, Petersenstrasse 32, 64287 Darmstadt, Germany
| | - Jan C Hellmann
- Technische Universität Darmstadt , Institute of Materials Science, Surface Science Division, Petersenstrasse 32, 64287 Darmstadt, Germany
| | - S David Tilley
- Ecole Polytechnique Fédérale de Lausanne (EPFL) , Institut des Sciences et Ingénierie Chimiques, Laboratory of Photonics and Interfaces, Station 6, CH-1015 Lausanne, Switzerland
| | - Michael Graetzel
- Ecole Polytechnique Fédérale de Lausanne (EPFL) , Institut des Sciences et Ingénierie Chimiques, Laboratory of Photonics and Interfaces, Station 6, CH-1015 Lausanne, Switzerland
| | - Jan Morasch
- Technische Universität Darmstadt , Institute of Materials Science, Surface Science Division, Petersenstrasse 32, 64287 Darmstadt, Germany
| | - Jonas Deuermeier
- i3N/CENIMAT, Universidade NOVA de Lisboa and CEMOP/UNINOVA , Department of Materials Science, Faculty of Science and Technology, Campus de Caparica, 2829-516 Caparica, Portugal
| | - Wolfram Jaegermann
- Technische Universität Darmstadt , Institute of Materials Science, Surface Science Division, Petersenstrasse 32, 64287 Darmstadt, Germany
| | - Andreas Klein
- Technische Universität Darmstadt , Institute of Materials Science, Surface Science Division, Petersenstrasse 32, 64287 Darmstadt, Germany
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28
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Modepalli V, Jin MJ, Park J, Jo J, Kim JH, Baik JM, Seo C, Kim J, Yoo JW. Gate-Tunable Spin Exchange Interactions and Inversion of Magnetoresistance in Single Ferromagnetic ZnO Nanowires. ACS NANO 2016; 10:4618-4626. [PMID: 26964013 DOI: 10.1021/acsnano.6b00921] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Electrical control of ferromagnetism in semiconductor nanostructures offers the promise of nonvolatile functionality in future semiconductor spintronics. Here, we demonstrate a dramatic gate-induced change of ferromagnetism in ZnO nanowire (NW) field-effect transistors (FETs). Ferromagnetism in our ZnO NWs arose from oxygen vacancies, which constitute deep levels hosting unpaired electron spins. The magnetic transition temperature of the studied ZnO NWs was estimated to be well above room temperature. The in situ UV confocal photoluminescence (PL) study confirmed oxygen vacancy mediated ferromagnetism in the studied ZnO NW FET devices. Both the estimated carrier concentration and temperature-dependent conductivity reveal the studied ZnO NWs are at the crossover of the metal-insulator transition. In particular, gate-induced modulation of the carrier concentration in the ZnO NW FET significantly alters carrier-mediated exchange interactions, which causes even inversion of magnetoresistance (MR) from negative to positive values. Upon sweeping the gate bias from -40 to +50 V, the MRs estimated at 2 K and 2 T were changed from -11.3% to +4.1%. Detailed analysis on the gate-dependent MR behavior clearly showed enhanced spin splitting energy with increasing carrier concentration. Gate-voltage-dependent PL spectra of an individual NW device confirmed the localization of oxygen vacancy-induced spins, indicating that gate-tunable indirect exchange coupling between localized magnetic moments played an important role in the remarkable change of the MR.
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Affiliation(s)
- Vijayakumar Modepalli
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan 689-798, Republic of Korea
| | - Mi-Jin Jin
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan 689-798, Republic of Korea
| | - Jungmin Park
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan 689-798, Republic of Korea
| | - Junhyeon Jo
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan 689-798, Republic of Korea
| | - Ji-Hyun Kim
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan 689-798, Republic of Korea
| | - Jeong Min Baik
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan 689-798, Republic of Korea
| | - Changwon Seo
- Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University , Suwon 440-746, Republic of Korea
- Department of Energy Science, Sungkyunkwan University , Suwon 440-746, Republic of Korea
| | - Jeongyong Kim
- Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University , Suwon 440-746, Republic of Korea
- Department of Energy Science, Sungkyunkwan University , Suwon 440-746, Republic of Korea
| | - Jung-Woo Yoo
- School of Materials Science and Engineering-Low dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology , Ulsan 689-798, Republic of Korea
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29
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Kelly LL, Racke DA, Schulz P, Li H, Winget P, Kim H, Ndione P, Sigdel AK, Brédas JL, Berry JJ, Graham S, Monti OLA. Spectroscopy and control of near-surface defects in conductive thin film ZnO. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:094007. [PMID: 26871256 DOI: 10.1088/0953-8984/28/9/094007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The electronic structure of inorganic semiconductor interfaces functionalized with extended π-conjugated organic molecules can be strongly influenced by localized gap states or point defects, often present at low concentrations and hard to identify spectroscopically. At the same time, in transparent conductive oxides such as ZnO, the presence of these gap states conveys the desirable high conductivity necessary for function as electron-selective interlayer or electron collection electrode in organic optoelectronic devices. Here, we report on the direct spectroscopic detection of a donor state within the band gap of highly conductive zinc oxide by two-photon photoemission spectroscopy. We show that adsorption of the prototypical organic acceptor C60 quenches this state by ground-state charge transfer, with immediate consequences on the interfacial energy level alignment. Comparison with computational results suggests the identity of the gap state as a near-surface-confined oxygen vacancy.
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Affiliation(s)
- Leah L Kelly
- University of Arizona, Department of Chemistry & Biochemistry, 1306 E. University Blvd., Tucson, Arizona 85721, USA
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30
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Xia C, Jiang Q, Zhao C, Hedhili MN, Alshareef HN. Selenide-Based Electrocatalysts and Scaffolds for Water Oxidation Applications. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2016; 28:77-85. [PMID: 26540620 DOI: 10.1002/adma.201503906] [Citation(s) in RCA: 251] [Impact Index Per Article: 31.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Revised: 09/30/2015] [Indexed: 05/03/2023]
Abstract
Selenide-based electrocatalysts and scaffolds on carbon cloth are successfully fabricated and demonstrated for enhanced water oxidation applications. A max-imum current density of 97.5 mA cm(-2) at an overpotential of a mere 300 mV and a small Tafel slope of 77 mV dec(-1) are achieved, suggesting the potential of these materials to serve as advanced oxygen evolution reaction catalysts.
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Affiliation(s)
- Chuan Xia
- Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Qiu Jiang
- Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Chao Zhao
- Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Mohamed N Hedhili
- Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
| | - Husam N Alshareef
- Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal, 23955-6900, Saudi Arabia
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31
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Opoku C, Dahiya AS, Oshman C, Daumont C, Cayrel F, Poulin-Vittrant G, Alquier D, Camara N. Fabrication of high performance field-effect transistors and practical Schottky contacts using hydrothermal ZnO nanowires. NANOTECHNOLOGY 2015; 26:355704. [PMID: 26245930 DOI: 10.1088/0957-4484/26/35/355704] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The production of large quantities of single crystalline semiconducting ZnO nanowires (NWs) at low cost can offer practical solutions to realizing several novel electronic/optoelectronic and sensor applications on an industrial scale. The present work demonstrates high-density single crystalline NWs synthesized by a multiple cycle hydrothermal process at ∼100 °C. The high carrier concentration in such ZnO NWs is greatly suppressed by a simple low cost thermal annealing step in ambient air at ∼450 °C. Single ZnO NW FETs incorporating these modified NWs are characterized, revealing strong metal work function-dependent charge transport, unobtainable with as-grown hydrothermal ZnO NWs. Single ZnO NW FETs with Al as source and drain (s/d) contacts show excellent performance metrics, including low off-state currents (fA range), high on/off ratio (10(5)-10(7)), steep subthreshold slope (<600 mV/dec) and excellent field-effect carrier mobility (5-11 cm(2)/V-s). Modified ZnO NWs with platinum s/d contacts demonstrate excellent Schottky transport characteristics, markedly different from a reference ZnO NW device with Al contacts. This included abrupt reverse bias current-voltage saturation characteristics and positive temperature coefficient (∼0.18 eV to 0.13 eV). This work is envisaged to benefit many areas of hydrothermal ZnO NW research, such as NW FETs, piezoelectric energy recovery, piezotronics and Schottky diodes.
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Affiliation(s)
- Charles Opoku
- Université François Rabelais de Tours, CNRS, GREMAN UMR 7347, 16 rue Pierre et Marie Curie, 37071 TOURS Cedex2, France
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32
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Jang JT, Park J, Ahn BD, Kim DM, Choi SJ, Kim HS, Kim DH. Study on the photoresponse of amorphous In-Ga-Zn-O and zinc oxynitride semiconductor devices by the extraction of sub-gap-state distribution and device simulation. ACS APPLIED MATERIALS & INTERFACES 2015; 7:15570-15577. [PMID: 26094854 DOI: 10.1021/acsami.5b04152] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Persistent photoconduction (PPC) is a phenomenon that limits the application of oxide semiconductor thin-film transistors (TFTs) in optical sensor-embedded displays. In the present work, a study on zinc oxynitride (ZnON) semiconductor TFTs based on the combination of experimental results and device simulation is presented. Devices incorporating ZnON semiconductors exhibit negligible PPC effects compared with amorphous In-Ga-Zn-O (a-IGZO) TFTs, and the difference between the two types of materials are examined by monochromatic photonic C-V spectroscopy (MPCVS). The latter method allows the estimation of the density of subgap states in the semiconductor, which may account for the different behavior of ZnON and IGZO materials with respect to illumination and the associated PPC. In the case of a-IGZO TFTs, the oxygen flow rate during the sputter deposition of a-IGZO is found to influence the amount of PPC. Small oxygen flow rates result in pronounced PPC, and large densities of valence band tail (VBT) states are observed in the corresponding devices. This implies a dependence of PPC on the amount of oxygen vacancies (VO). On the other hand, ZnON has a smaller bandgap than a-IGZO and contains a smaller density of VBT states over the entire range of its bandgap energy. Here, the concept of activation energy window (AEW) is introduced to explain the occurrence of PPC effects by photoinduced electron doping, which is likely to be associated with the formation of peroxides in the semiconductor. The analytical methodology presented in this report accounts well for the reduction of PPC in ZnON TFTs, and provides a quantitative tool for the systematic development of phototransistors for optical sensor-embedded interactive displays.
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Affiliation(s)
- Jun Tae Jang
- †School of Electrical Engineering, Kookmin University, Seoul 136-702, Republic of Korea
| | - Jozeph Park
- ‡Department of Materials Science and Engineering, KAIST, Daejeon 305-338, Republic of Korea
| | - Byung Du Ahn
- §School of Electrical and Electronic Engineering, Yonsei University, Seoul 120-749, Republic of Korea
| | - Dong Myong Kim
- †School of Electrical Engineering, Kookmin University, Seoul 136-702, Republic of Korea
| | - Sung-Jin Choi
- †School of Electrical Engineering, Kookmin University, Seoul 136-702, Republic of Korea
| | - Hyun-Suk Kim
- #Department of Materials Science and Engineering, Chungnam National University, Daejeon 305-764, Republic of Korea
| | - Dae Hwan Kim
- †School of Electrical Engineering, Kookmin University, Seoul 136-702, Republic of Korea
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33
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Santana JA, Krogel JT, Kim J, Kent PRC, Reboredo FA. Structural stability and defect energetics of ZnO from diffusion quantum Monte Carlo. J Chem Phys 2015; 142:164705. [DOI: 10.1063/1.4919242] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Juan A. Santana
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Jaron T. Krogel
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Jeongnim Kim
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Paul R. C. Kent
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
- Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - Fernando A. Reboredo
- Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
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34
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Socratous J, Banger KK, Vaynzof Y, Sadhanala A, Brown AD, Sepe A, Steiner U, Sirringhaus H. Electronic Structure of Low-Temperature Solution-Processed Amorphous Metal Oxide Semiconductors for Thin-Film Transistor Applications. ADVANCED FUNCTIONAL MATERIALS 2015; 25:1873-1885. [PMID: 26190964 PMCID: PMC4503976 DOI: 10.1002/adfm.201404375] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2014] [Revised: 01/28/2015] [Indexed: 05/20/2023]
Abstract
The electronic structure of low temperature, solution-processed indium-zinc oxide thin-film transistors is complex and remains insufficiently understood. As commonly observed, high device performance with mobility >1 cm2 V-1 s-1 is achievable after annealing in air above typically 250 °C but performance decreases rapidly when annealing temperatures ≤200 °C are used. Here, the electronic structure of low temperature, solution-processed oxide thin films as a function of annealing temperature and environment using a combination of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and photothermal deflection spectroscopy is investigated. The drop-off in performance at temperatures ≤200 °C to incomplete conversion of metal hydroxide species into the fully coordinated oxide is attributed. The effect of an additional vacuum annealing step, which is beneficial if performed for short times at low temperatures, but leads to catastrophic device failure if performed at too high temperatures or for too long is also investigated. Evidence is found that during vacuum annealing, the workfunction increases and a large concentration of sub-bandgap defect states (re)appears. These results demonstrate that good devices can only be achieved in low temperature, solution-processed oxides if a significant concentration of acceptor states below the conduction band minimum is compensated or passivated by shallow hydrogen and oxygen vacancy-induced donor levels.
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Affiliation(s)
| | | | - Yana Vaynzof
- Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK
| | - Aditya Sadhanala
- Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK
| | - Adam D Brown
- Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK
| | - Alessandro Sepe
- Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK
| | - Ullrich Steiner
- Cavendish Laboratory 19 JJ Thomson Avenue, CB3 OHE, Cambridge, UK
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35
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Bandopadhyay K, Mitra J. Zn interstitials and O vacancies responsible for n-type ZnO: what do the emission spectra reveal? RSC Adv 2015. [DOI: 10.1039/c5ra00355e] [Citation(s) in RCA: 123] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Evidencing interstitial Zn related defect states inside the conduction band of Zn-rich ZnO nanorods.
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Affiliation(s)
- K. Bandopadhyay
- School of Physics
- Indian Institute of Science Education and Research Thiruvananthapuram
- Thiruvananthapuram 695016
- India
| | - J. Mitra
- School of Physics
- Indian Institute of Science Education and Research Thiruvananthapuram
- Thiruvananthapuram 695016
- India
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36
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Pradel KC, Wu W, Ding Y, Wang ZL. Solution-derived ZnO homojunction nanowire films on wearable substrates for energy conversion and self-powered gesture recognition. NANO LETTERS 2014; 14:6897-6905. [PMID: 25423258 DOI: 10.1021/nl5029182] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Emerging applications in wearable technology, pervasive computing, human-machine interfacing, and implantable biomedical devices demand an appropriate power source that can sustainably operate for extended periods of time with minimal intervention (Wang, Z. L.; et al. Angew. Chem., Int. Ed. 2012, 51, 11700). Self-powered nanosystems, which harvest operating energy from its host (i.e., the human body), may be feasible due to their extremely low power consumption (Tian, B. Z.; et al. Nature 2007, 449, 885. Javey, A.; et al. Nature 2003, 424, 654. Cui, Y.; et al. Science 2001, 291, 851). Here we report materials and designs for wearable-on-skin piezoelectric devices based on ultrathin (2 μm) solution-derived ZnO p-n homojunction films for the first time. The depletion region formed at the p-n homojunction effectively reduces internal screening of strain-induced polarization charges by free carriers in both n-ZnO and Sb-doped p-ZnO, resulting in significantly enhanced piezoelectric output compared to a single layer device. The p-n structure can be further grown on polymeric substrates conformable to a human wrist and used to convert movement of the flexor tendons into distinguishable electrical signals for gesture recognition. The ZnO homojunction piezoelectric devices may have applications in powering nanodevices, bioprobes, and self-powered human-machine interfacing.
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Affiliation(s)
- Ken C Pradel
- School of Materials Science and Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332-0245, United States
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37
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Kan E, Deng K, Wu F. Stability of graphitic-like zinc oxide layers under carriers doping: a first-principles study. NANOSCALE 2013; 5:12111-12114. [PMID: 24145368 DOI: 10.1039/c3nr04845d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Although theoretical works have demonstrated that (0001) polar films of wurtzite (WZ) ZnO automatically transform into graphitic-like (GP) structures, the experimental realization of GP ZnO is limited to a thickness of several atomic layers. Here, using first-principles calculations, we demonstrated that the stability of GP ZnO is closely related to the concentration of near-free carriers. Our results show that the doped carriers, originating from the rich oxygen vacancies, can effectively screen the polar field, and stabilize the WZ structure. Thus, in order to obtain GP ZnO layers with much thicker films, it is necessary to reduce the near-free carrier concentration.
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Affiliation(s)
- Erjun Kan
- Key Laboratory of Soft Chemistry and Functional Materials, Ministry of Education, Department of Applied Physics, Nanjing University of Science and Technology, Nanjing, Jiangsu 210094, P.R. China.
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38
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39
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Fang Y, Wang Y, Gu L, Lu R, Sha J. Effect of the defect on photoluminescence property of Al-coated ZnO nanostructures. OPTICS EXPRESS 2013; 21:3492-3500. [PMID: 23481807 DOI: 10.1364/oe.21.003492] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The room-temperature photoluminescence (PL) spectra of hydrothermal grown ZnO film and nanowires coated with Al are investigated, which exhibit much less UV emission enhancement ratio as against that of nanowires fabricated by thermal evaporation method. A model is suggested at last to interpret the experimental results considering the influence of the defect on the contact property between metal and ZnO, which is further evidenced by the weak PL enhancement ratio of thermal evaporation grown ZnO nanowires with H(2)O(2) treatment.
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Affiliation(s)
- Yanjun Fang
- Department of Physics & State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou 310027, China
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40
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Wan W, Huang J, Zhu L, Hu L, Wen Z, Sun L, Ye Z. Defects induced ferromagnetism in ZnO nanowire arrays doped with copper. CrystEngComm 2013. [DOI: 10.1039/c3ce40819a] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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41
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Iza DC, Muñoz-Rojas D, Jia Q, Swartzentruber B, MacManus-Driscoll JL. Tuning of defects in ZnO nanorod arrays used in bulk heterojunction solar cells. NANOSCALE RESEARCH LETTERS 2012; 7:655. [PMID: 23186280 PMCID: PMC3533996 DOI: 10.1186/1556-276x-7-655] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Accepted: 11/14/2012] [Indexed: 05/07/2023]
Abstract
With particular focus on bulk heterojunction solar cells incorporating ZnO nanorods, we study how different annealing environments (air or Zn environment) and temperatures impact on the photoluminescence response. Our work gives new insight into the complex defect landscape in ZnO, and it also shows how the different defect types can be manipulated. We have determined the emission wavelengths for the two main defects which make up the visible band, the oxygen vacancy emission wavelength at approximately 530 nm and the zinc vacancy emission wavelength at approximately 630 nm. The precise nature of the defect landscape in the bulk of the nanorods is found to be unimportant to photovoltaic cell performance although the surface structure is more critical. Annealing of the nanorods is optimum at 300°C as this is a sufficiently high temperature to decompose Zn(OH)2 formed at the surface of the nanorods during electrodeposition and sufficiently low to prevent ITO degradation.
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Affiliation(s)
- Diana C Iza
- Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, UK
| | - David Muñoz-Rojas
- Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, UK
| | - Quanxi Jia
- MPA CINT, MS K771, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
| | - Brian Swartzentruber
- Sandia National Laboratories, MS 1303.1515 Eubank SE, Albuquerque, NM 87123, USA
| | - Judith L MacManus-Driscoll
- Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, UK
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42
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Mohan R, Krishnamoorthy K, Kim SJ. Diameter dependent photocatalytic activity of ZnO nanowires grown by vapor transport technique. Chem Phys Lett 2012. [DOI: 10.1016/j.cplett.2012.04.054] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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43
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Zheng H, Kröger J, Berndt R. Spectroscopy of single donors at ZnO(0001) surfaces. PHYSICAL REVIEW LETTERS 2012; 108:076801. [PMID: 22401235 DOI: 10.1103/physrevlett.108.076801] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2011] [Indexed: 05/31/2023]
Abstract
Donors near the polar (0001) surface of nominally undoped ZnO were investigated with scanning tunneling microscopy at 5 K. Spatially resolved spectroscopy reveals single and double charging. Equidistant peaks in spectra of ionized donors are attributed to polaron excitation. The data are consistent with doping due to Zn interstitials or complexes.
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Affiliation(s)
- Hao Zheng
- Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, Kiel, Germany.
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44
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Lany S, Zakutayev A, Mason TO, Wager JF, Poeppelmeier KR, Perkins JD, Berry JJ, Ginley DS, Zunger A. Surface origin of high conductivities in undoped In2O3 thin films. PHYSICAL REVIEW LETTERS 2012; 108:016802. [PMID: 22304278 DOI: 10.1103/physrevlett.108.016802] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/06/2011] [Indexed: 05/31/2023]
Abstract
The microscopic cause of conductivity in transparent conducting oxides like ZnO, In{2}O{3}, and SnO{2} is generally considered to be a point defect mechanism in the bulk, involving intrinsic lattice defects, extrinsic dopants, or unintentional impurities like hydrogen. We confirm here that the defect theory for O-vacancies can quantitatively account for the rather moderate conductivity and off-stoichiometry observed in bulk In{2}O{3} samples under high-temperature equilibrium conditions. However, nominally undoped thin-films of In{2}O{3} can exhibit surprisingly high conductivities exceeding by 4-5 orders of magnitude that of bulk samples under identical conditions (temperature and O{2} partial pressure). Employing surface calculations and thickness-dependent Hall measurements, we demonstrate that surface donors rather than bulk defects dominate the conductivity of In{2}O{3} thin films.
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Affiliation(s)
- S Lany
- National Renewable Energy Laboratory, Golden, Colorado 80401, USA
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Cha SY, Shin JM, Kim SJ, Park SE, Cho CR, Cho YC, Jeong SY. Improving the precision of Hall effect measurements using a single-crystal copper probe. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2012; 83:013901. [PMID: 22299964 DOI: 10.1063/1.3677333] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The circuitry and components of a Hall measurement kit were replaced with single-crystal copper (SCC) wires and parts prepared by a novel wire fabrication process. This process preserved the grain-free structure of SCC grown by the Czochralski method. The new kit was used to determine, with greatly improved precision, the electrical coefficients such as carrier density and mobility, establish the reproducibility of the measured values, and define the semiconductor type. The observed reduction in electrical signal losses and distortion has been attributed to grain boundary elimination.
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Affiliation(s)
- Su-Young Cha
- Department of Nano Fusion Technology, Pusan National University, Miryang, South Korea
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Na CW, Woo HS, Kim HJ, Jeong U, Chung JH, Lee JH. Controlled transformation of ZnO nanobelts into CoO/Co3O4 nanowires. CrystEngComm 2012. [DOI: 10.1039/c2ce06681e] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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47
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Kälblein D, Weitz RT, Böttcher HJ, Ante F, Zschieschang U, Kern K, Klauk H. Top-gate ZnO nanowire transistors and integrated circuits with ultrathin self-assembled monolayer gate dielectric. NANO LETTERS 2011; 11:5309-5315. [PMID: 22029286 DOI: 10.1021/nl202767h] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
A novel approach for the fabrication of transistors and circuits based on individual single-crystalline ZnO nanowires synthesized by a low-temperature hydrothermal method is reported. The gate dielectric of these transistors is a self-assembled monolayer that has a thickness of 2 nm and efficiently isolates the ZnO nanowire from the top-gate electrodes. Inverters fabricated on a single ZnO nanowire operate with frequencies up to 1 MHz. Compared with metal-semiconductor field-effect transistors, in which the isolation of the gate electrode from the carrier channel relies solely on the depletion layer in the semiconductor, the self-assembled monolayer dielectric leads to a reduction of the gate current by more than 3 orders of magnitude.
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Affiliation(s)
- Daniel Kälblein
- Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany.
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Wong KM, Fang Y, Devaux A, Wen L, Huang J, De Cola L, Lei Y. Assorted analytical and spectroscopic techniques for the optimization of the defect-related properties in size-controlled ZnO nanowires. NANOSCALE 2011; 3:4830-9. [PMID: 21986965 DOI: 10.1039/c1nr10806a] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
In this article, the important role of the intrinsic defects in size-controlled ZnO nanowires (NWs) which play a critical role in the properties of the NWs, was studied with a combined innovative experimental analysis. The NWs prepared by both the aqueous solution method and chemical vapour deposition process were of increasing length and decreasing size-to-volume (S/V) ratio. The combined approach involved different analytical and spectroscopic techniques and from the correlation between the different measurements, the concentration of the oxygen vacancies jointly with the zinc interstitials defects and the zinc vacancy defects was observed to be positively or negatively correlated, respectively, with the magnitude of the photoluminescence intensity and radiative lifetimes. Furthermore, the experimental results also suggest that the oxygen vacancy defects are not only spatially located on the surface of the NW but an increasing fraction of the total oxygen vacancy defects connected with the green emission is also located in an annulus region beneath the surface as the ZnO NWs elongate. On the other hand, as the donor concentration plays a critical function in the properties of the ZnO NWs, an analytical model was derived for the calculation of the donor concentration of the NWs directly from its reverse-biased current-voltage characteristics obtained from the conductive atomic force microscopy measurements.
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Affiliation(s)
- Kin Mun Wong
- Institute of Materials Physics and Center for Nanotechnology, University of Muenster, Wilhelm-Klemm-Str. 10, 48149, Muenster, Germany
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King PDC, Veal TD. Conductivity in transparent oxide semiconductors. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2011; 23:334214. [PMID: 21813954 DOI: 10.1088/0953-8984/23/33/334214] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Despite an extensive research effort for over 60 years, an understanding of the origins of conductivity in wide band gap transparent conducting oxide (TCO) semiconductors remains elusive. While TCOs have already found widespread use in device applications requiring a transparent contact, there are currently enormous efforts to (i) increase the conductivity of existing materials, (ii) identify suitable alternatives, and (iii) attempt to gain semiconductor-engineering levels of control over their carrier density, essential for the incorporation of TCOs into a new generation of multifunctional transparent electronic devices. These efforts, however, are dependent on a microscopic identification of the defects and impurities leading to the high unintentional carrier densities present in these materials. Here, we review recent developments towards such an understanding. While oxygen vacancies are commonly assumed to be the source of the conductivity, there is increasing evidence that this is not a sufficient mechanism to explain the total measured carrier concentrations. In fact, many studies suggest that oxygen vacancies are deep, rather than shallow, donors, and their abundance in as-grown material is also debated. We discuss other potential contributions to the conductivity in TCOs, including other native defects, their complexes, and in particular hydrogen impurities. Convincing theoretical and experimental evidence is presented for the donor nature of hydrogen across a range of TCO materials, and while its stability and the role of interstitial versus substitutional species are still somewhat open questions, it is one of the leading contenders for yielding unintentional conductivity in TCOs. We also review recent work indicating that the surfaces of TCOs can support very high carrier densities, opposite to the case for conventional semiconductors. In thin-film materials/devices and, in particular, nanostructures, the surface can have a large impact on the total conductivity in TCOs. We discuss models that attempt to explain both the bulk and surface conductivity on the basis of bulk band structure features common across the TCOs, and compare these materials to other semiconductors. Finally, we briefly consider transparency in these materials, and its interplay with conductivity. Understanding this interplay, as well as the microscopic contenders for providing the conductivity of these materials, will prove essential to the future design and control of TCO semiconductors, and their implementation into novel multifunctional devices.
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Affiliation(s)
- P D C King
- School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS, UK.
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Oba F, Choi M, Togo A, Tanaka I. Point defects in ZnO: an approach from first principles. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2011; 12:034302. [PMID: 27877390 PMCID: PMC5090462 DOI: 10.1088/1468-6996/12/3/034302] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2011] [Revised: 05/27/2011] [Accepted: 03/16/2011] [Indexed: 05/03/2023]
Abstract
Recent first-principles studies of point defects in ZnO are reviewed with a focus on native defects. Key properties of defects, such as formation energies, donor and acceptor levels, optical transition energies, migration energies and atomic and electronic structure, have been evaluated using various approaches including the local density approximation (LDA) and generalized gradient approximation (GGA) to DFT, LDA+U/GGA+U, hybrid Hartree-Fock density functionals, sX and GW approximation. Results significantly depend on the approximation to exchange correlation, the simulation models for defects and the post-processes to correct shortcomings of the approximation and models. The choice of a proper approach is, therefore, crucial for reliable theoretical predictions. First-principles studies have provided an insight into the energetics and atomic and electronic structures of native point defects and impurities and defect-induced properties of ZnO. Native defects that are relevant to the n-type conductivity and the non-stoichiometry toward the O-deficient side in reduced ZnO have been debated. It is suggested that the O vacancy is responsible for the non-stoichiometry because of its low formation energy under O-poor chemical potential conditions. However, the O vacancy is a very deep donor and cannot be a major source of carrier electrons. The Zn interstitial and anti-site are shallow donors, but these defects are unlikely to form at a high concentration in n-type ZnO under thermal equilibrium. Therefore, the n-type conductivity is attributed to other sources such as residual impurities including H impurities with several atomic configurations, a metastable shallow donor state of the O vacancy, and defect complexes involving the Zn interstitial. Among the native acceptor-type defects, the Zn vacancy is dominant. It is a deep acceptor and cannot produce a high concentration of holes. The O interstitial and anti-site are high in formation energy and/or are electrically inactive and, hence, are unlikely to play essential roles in electrical properties. Overall defect energetics suggests a preference for the native donor-type defects over acceptor-type defects in ZnO. The O vacancy, Zn interstitial and Zn anti-site have very low formation energies when the Fermi level is low. Therefore, these defects are expected to be sources of a strong hole compensation in p-type ZnO. For the n-type doping, the compensation of carrier electrons by the native acceptor-type defects can be mostly suppressed when O-poor chemical potential conditions, i.e. low O partial pressure conditions, are chosen during crystal growth and/or doping.
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Affiliation(s)
- Fumiyasu Oba
- Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan
| | - Minseok Choi
- Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan
| | - Atsushi Togo
- Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan
| | - Isao Tanaka
- Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501, Japan
- Nanostructures Research Laboratory, Japan Fine Ceramics Center, Atsuta, Nagoya 456-8587, Japan
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