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Vijay NK, Maya PN, Mukherjee S, Liedke MO, Butterling M, Attallah AG, Hirschmann E, Wagner A, Benoy MD. Effect of annealing temperature on the structure and optical properties of ZnO thin films. J Phys Condens Matter 2023; 36:135002. [PMID: 38061063 DOI: 10.1088/1361-648x/ad1361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/09/2023] [Accepted: 12/07/2023] [Indexed: 12/22/2023]
Abstract
The effect of annealing temperature on the microstructure, defects and optical properties of ZnO thin films are investigated using sol-gel based spin coating method for a range of annealing temperatures from 200∘C to 500∘C. The correlation among the microstructure, defects, impurity content and the optical band gap of films of thickness about 10-12 nm is elucidated. The particle size increases and the optical band gap reduces with the annealing temperature. At 200∘C, amorphous films were formed with particle size less than 10 nm with an optical band gap of about 3.41 eV. As the temperature increases the grain size increases and the defect, impurity content as well as the optical band gap reduces. This could be due to the reduction in the lattice strain. For an average grain size of about 35 nm and above, the band gap asymptotically approaches the theoretical value of ZnO (3.37 eV). The photoluminescence (PL) spectra show a systematic red-shift in the excitonic levels corresponding to the variation in the optical band-gap. The defect emission from Zn-vacancies is observed in the PL spectra and are further supported by the positron annihilation measurements.
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Affiliation(s)
| | - P N Maya
- Institute for Plasma Research, Bhat, Gandhinagar 382428, India
| | - S Mukherjee
- Bhabha Atomic Research Center, Trombay, Mumbai 400085, India
| | - M O Liedke
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics, Bautzner Landstraße, 400, 01328 Dresden, Germany
| | - M Butterling
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics, Bautzner Landstraße, 400, 01328 Dresden, Germany
| | - A G Attallah
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics, Bautzner Landstraße, 400, 01328 Dresden, Germany
| | - E Hirschmann
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics, Bautzner Landstraße, 400, 01328 Dresden, Germany
| | - A Wagner
- Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiation Physics, Bautzner Landstraße, 400, 01328 Dresden, Germany
| | - M D Benoy
- Mar Athanasius College, Kothamangalam 686666, India
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Huang SM, Lai MJ, Liu RS, Liu TY, Lin RM. Strain Compensation and Trade-Off Design Result in Exciton Emission at 306 nm from AlGaN LEDs at Temperatures up to 368 K. Materials (Basel) 2021; 14:6699. [PMID: 34772224 DOI: 10.3390/ma14216699] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 11/04/2021] [Accepted: 11/05/2021] [Indexed: 11/24/2022]
Abstract
In this study, we suppressed the parasitic emission caused by electron overflow found in typical ultraviolet B (UVB) and ultraviolet C (UVC) light-emitting diodes (LEDs). The modulation of the p-layer structure and aluminum composition as well as a trade-off in the structure to ensure strain compensation allowed us to increase the p-AlGaN doping efficiency and hole numbers in the p-neutral region. This approach led to greater matching of the electron and hole numbers in the UVB and UVC emission quantum wells. Our UVB LED (sample A) exhibited clear exciton emission, with its peak near 306 nm, and a band-to-band emission at 303 nm. The relative intensity of the exciton emission of sample A decreased as a result of the thermal energy effect of the temperature increase. Nevertheless, sample A displayed its exciton emission at temperatures of up to 368 K. In contrast, our corresponding UVC LED (sample B) only exhibited a Gaussian peak emission at a wavelength of approximately 272 nm.
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Zhang D, Gan L, Zhang J, Zhang R, Wang Z, Feng J, Sun H, Ning CZ. Reconstructing Local Profile of Exciton-Emission Wavelengths across a WS 2 Bubble beyond the Diffraction Limit. ACS Nano 2020; 14:6931-6937. [PMID: 32491830 DOI: 10.1021/acsnano.0c01337] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Air bubbles formed between layers of two-dimensional (2D) materials not only are unavoidable but also emerge as an important means of engineering their excitonic emission properties, especially as controllable quantum light sources. Measuring the actual spatially resolved optical properties across such bubbles is important for understanding excitonic physics and for device applications; however, such a measurement is challenging due to nanoscale features involved which require spatial resolution beyond the diffraction limit. Additional complexity is the involvement of multiple physical effects such as mechanical strain and dielectric environment that are difficult to disentangle. In this paper, we demonstrate an effective approach combining micro-photoluminescence measurement, atomic force microscope profile mapping, and a theoretical strain model. We succeeded in reconstructing the actual spatial profiles of the emission wavelengths beyond the diffraction limit for bubbles formed by a monolayer tungsten disulfide on boron nitride. The agreements and consistency among various approaches established the validity of our approach. In addition, our approach allows us to disentangle the effects of strain and dielectric environment and provides a general and reliable method to determine the true magnitude of wavelength changes due to the individual effects across bubbles. Importantly, we found that micro-optical measurement underestimates the red and blue shifts by almost 5 times. Our results provide important insights into strain and screening-dependent optical properties of 2D materials on the nanometer scale and contribute significantly to our understanding of excitonic emission physics as well as potential applications of bubbles in optoelectronic devices.
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Affiliation(s)
- Danyang Zhang
- Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
- International Center for Nano-Optoelectronics, Tsinghua University, Beijing 100084, China
| | - Lin Gan
- Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
- International Center for Nano-Optoelectronics, Tsinghua University, Beijing 100084, China
- Beijing National Research Center for Information Science and Technology, Beijing 100084, China
| | - Jianxing Zhang
- Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
- International Center for Nano-Optoelectronics, Tsinghua University, Beijing 100084, China
| | - Ruiling Zhang
- Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
- International Center for Nano-Optoelectronics, Tsinghua University, Beijing 100084, China
| | - Zhen Wang
- Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
- International Center for Nano-Optoelectronics, Tsinghua University, Beijing 100084, China
| | - Jiabin Feng
- Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
- International Center for Nano-Optoelectronics, Tsinghua University, Beijing 100084, China
| | - Hao Sun
- Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
- International Center for Nano-Optoelectronics, Tsinghua University, Beijing 100084, China
- Beijing National Research Center for Information Science and Technology, Beijing 100084, China
| | - Cun-Zheng Ning
- Department of Electronic Engineering, Tsinghua University, Beijing 100084, China
- Frontier Science Center for Quantum Information, Beijing 100084, China
- International Center for Nano-Optoelectronics, Tsinghua University, Beijing 100084, China
- Beijing National Research Center for Information Science and Technology, Beijing 100084, China
- School of Electrical, Computer, and Energy Engineering, Arizona State University, Tempe, Arizona 85287, United States
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