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Chiu NC, Smith KT, Stylianou KC. Metal-organic frameworks for white light emission: From synthesis to device fabrication. Coord Chem Rev 2022. [DOI: 10.1016/j.ccr.2022.214441] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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Thermophysical Characterization of Efficiency Droop in GaN-Based Light-Emitting Diodes. NANOMATERIALS 2021; 11:nano11061449. [PMID: 34070771 PMCID: PMC8227426 DOI: 10.3390/nano11061449] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 05/18/2021] [Accepted: 05/27/2021] [Indexed: 11/16/2022]
Abstract
An efficiency droop in GaN-based light-emitting diodes (LED) was characterized by examining its general thermophysical parameters. An effective suppression of emission degradation afforded by the introduction of InGaN/GaN heterobarrier structures in the active region was attributable to an increase in the capture cross-section ratios. The Debye temperatures and the electron–phonon interaction coupling coefficients were obtained from temperature-dependent current-voltage measurements of InGaN/GaN multiple-quantum-well LEDs over a temperature range from 20 to 300 K. It was found that the Debye temperature of the LEDs was modulated by the InN molar fraction in the heterobarriers. As far as the phonons involved in the electron–phonon scattering process are concerned, the average number of phonons decreases with the Debye temperature, and the electron–phonon interaction coupling coefficients phenomenologically reflect the nonradiative transition rates. We can use the characteristic ratio of the Debye temperature to the coupling coefficient (DCR) to assess the efficiency droop phenomenon. Our investigation showed that DCR is correlated to quantum efficiency (QE). The light emission results exhibited the high and low QEs to be represented by the high and low DCRs associated with low and high injection currents, respectively. The DCR can be envisioned as a thermophysical marker of LED performance, not only for efficiency droop characterization but also for heterodevice structure optimization.
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Chaste J, Hnid I, Khalil L, Si C, Durnez A, Lafosse X, Zhao MQ, Johnson ATC, Zhang S, Bang J, Ouerghi A. Phase Transition in a Memristive Suspended MoS 2 Monolayer Probed by Opto- and Electro-Mechanics. ACS NANO 2020; 14:13611-13618. [PMID: 33054170 DOI: 10.1021/acsnano.0c05721] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Semiconducting monolayers of a 2D material are able to concatenate multiple interesting properties into a single component. Here, by combining opto-mechanical and electronic measurements, we demonstrate the presence of a partial 2H-1T' phase transition in a suspended 2D monolayer membrane of MoS2. Electronic transport shows unexpected memristive properties in the MoS2 membrane, in the absence of any external dopants. A strong mechanical softening of the membrane is measured concurrently and may only be related to the 2H-1T' phase transition, which imposes a 3% directional elongation of the topological 1T' phase with respect to the semiconducting 2H. We note that only a few percent 2H-1T' phase switching is sufficient to observe measurable memristive effects. Our experimental results combined with first-principles total energy calculations indicate that sulfur vacancy diffusion plays a key role in the initial nucleation of the phase transition. Our study clearly shows that nanomechanics represents an ultrasensitive technique to probe the crystal phase transition in 2D materials or thin membranes. Finally, a better control of the microscopic mechanisms responsible for the observed memristive effect in MoS2 is important for the implementation of future devices.
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Affiliation(s)
- Julien Chaste
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, 91120, Palaiseau, France
| | - Imen Hnid
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, 91120, Palaiseau, France
| | - Lama Khalil
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, 91120, Palaiseau, France
| | - Chen Si
- School of Materials Science and Engineering, Beihang University, Beijing 100191, China
| | - Alan Durnez
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, 91120, Palaiseau, France
| | - Xavier Lafosse
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, 91120, Palaiseau, France
| | - Meng-Qiang Zhao
- Department of Physics and Astronomy, University of Pennsylvania, 209S 33rd Street, Philadelphia, Pennsylvania 19104, United States
| | - A T Charlie Johnson
- Department of Physics and Astronomy, University of Pennsylvania, 209S 33rd Street, Philadelphia, Pennsylvania 19104, United States
| | - Shengbai Zhang
- Department of Physics, Applied Physics, & Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180, United States
| | - Junhyeok Bang
- Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
| | - Abdelkarim Ouerghi
- Université Paris-Saclay, CNRS, Centre de Nanosciences et de Nanotechnologies, 91120, Palaiseau, France
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Si C, Choe D, Xie W, Wang H, Sun Z, Bang J, Zhang S. Photoinduced Vacancy Ordering and Phase Transition in MoTe 2. NANO LETTERS 2019; 19:3612-3617. [PMID: 31096752 DOI: 10.1021/acs.nanolett.9b00613] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We show that non-equilibrium dynamics plays a central role in the photoinduced 2H-to-1T' phase transition of MoTe2. The phase transition is initiated by a local ordering of Te vacancies, followed by a 1T' structural change in the original 2H lattice. The local 1T' region serves as a seed to gather more vacancies into ordering and subsequently induces a further growth of the 1T' phase. Remarkably, this process is controlled by photogenerated excited carriers as they enhance vacancy diffusion, increase the speed of vacancy ordering, and are hence vital to the 1T' phase transition. This mechanism can be contrasted to the current model requiring a collective sliding of a whole Te atomic layer, which is thermodynamically highly unlikely. By uncovering the key roles of photoexcitations, our results may have important implications for finely controlling phase transitions in transition metal dichalcogenides.
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Affiliation(s)
- Chen Si
- School of Materials Science and Engineering , Beihang University , Beijing 100191 , People's Republic of China
- Department of Physics, Applied Physics, & Astronomy , Rensselaer Polytechnic Institute , Troy , New York 12180 , United States
| | - Dukhyun Choe
- Department of Physics, Applied Physics, & Astronomy , Rensselaer Polytechnic Institute , Troy , New York 12180 , United States
| | - Weiyu Xie
- Department of Physics, Applied Physics, & Astronomy , Rensselaer Polytechnic Institute , Troy , New York 12180 , United States
| | - Han Wang
- Department of Physics, Applied Physics, & Astronomy , Rensselaer Polytechnic Institute , Troy , New York 12180 , United States
| | - Zhimei Sun
- School of Materials Science and Engineering , Beihang University , Beijing 100191 , People's Republic of China
| | - Junhyeok Bang
- Spin Engineering Physics Team , Korea Basic Science Institute (KBSI) , Daejeon 305-806 , Republic of Korea
| | - Shengbai Zhang
- Department of Physics, Applied Physics, & Astronomy , Rensselaer Polytechnic Institute , Troy , New York 12180 , United States
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Electrically driven, highly efficient three-dimensional GaN-based light emitting diodes fabricated by self-aligned twofold epitaxial lateral overgrowth. Sci Rep 2017; 7:9663. [PMID: 28852044 PMCID: PMC5575063 DOI: 10.1038/s41598-017-10086-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2017] [Accepted: 08/02/2017] [Indexed: 11/17/2022] Open
Abstract
Improvements in the overall efficiency and significant reduction in the efficiency droop are observed in three-dimensional (3D) GaN truncated pyramid structures fabricated with air void and a SiO2 layer. This 3D structure was fabricated using a self-aligned twofold epitaxial lateral overgrowth technique, which improved both the internal quantum efficiency and the light extraction efficiency. In addition, a reduced leakage current was observed due to the effective suppression of threading dislocations. While this study focuses primarily on the blue emission wavelength region, this approach can also be applied to overcome the efficiency degradation problem in the ultraviolet, green, and red emission regions.
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Chen NK, Han D, Li XB, Liu F, Bang J, Wang XP, Chen QD, Wang HY, Zhang S, Sun HB. Giant lattice expansion by quantum stress and universal atomic forces in semiconductors under instant ultrafast laser excitation. Phys Chem Chem Phys 2017; 19:24735-24741. [DOI: 10.1039/c7cp03103c] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Electronic excitation induced stress and force may provide a new route to manipulate the structure of materials using ultrafast lasers.
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