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Vögl F, Avramescu A, Gelfert S, Lex A, Waag A, Hetzl M, von Malm N. Optical characteristics of thin film-based InGaN micro-LED arrays: a study on size effect and far field behavior. OPTICS EXPRESS 2024; 32:17644-17656. [PMID: 38858942 DOI: 10.1364/oe.523274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2024] [Accepted: 04/19/2024] [Indexed: 06/12/2024]
Abstract
Micro-light emitting diodes (µ-LEDs) are considered the key enabler for various high-resolution micro-display applications such as augmented reality, smartphones or head-up displays. Within this study we fabricated nitride-based µ-LED arrays in a thin film chip architecture with lateral pixel sizes down to 1 µm. A metal mirror on the p-side enhances the light outcoupling via the n-side after removal of the epitaxial growth substrate. Mounted devices with pixel sizes ranging from 1×1 to 8×8 µm2 were electro-optically characterized within an integrating sphere and in a goniometer system. We measure increased external quantum efficiencies on smaller devices due to a higher light extraction efficiency (LEE) as predicted by wave optical simulations. Besides this size dependence of the LEE, also the far field properties show a substantial change with pixel size. In addition, we compared µ-LEDs with 40 nm and 80 nm thick aluminium oxide around the pixel mesa. Considerably different far field patterns were observed which indicate the sensitivity of optical properties to any design changes for tiny µ-LEDs. The experimentally obtained radiation behavior could be reasonably predicted by finite-difference time-domain simulations. This clearly reveals the importance of understanding and modeling wave optical effects inside µ-LED devices and the resulting impact on their optical performance.
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Zhu J, Hu S, Chen B, Wei S, Zhang Y, Wu X, Zou X, Lu X, Sun Q, Zhang DW, Ji L. Realization of tunable-performance in atomic layer deposited Hf-doped In2O3 thin film transistor via oxygen vacancy modulation. J Chem Phys 2024; 160:044706. [PMID: 38270240 DOI: 10.1063/5.0188101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2023] [Accepted: 01/05/2024] [Indexed: 01/26/2024] Open
Abstract
Due to the limitation of inherent ultra-high electron concentration, the electrical properties of In2O3 resemble those of conductors rather than semiconductors prior to special treatment. In this study, the effect of various annealing treatments on the microstructure, optical properties, and oxygen vacancies of the films and transistors is systematically investigated. Our finding reveals a progressive crystallization trend in the films with increasing annealing temperature. In addition, a higher annealing temperature is also associated with the reduction in the concentration of oxygen vacancies, as well as an elevation in both optical transmittance and optical bandgap. Furthermore, with the implementation of annealing process, the devices gradually transform from no pronounced gate control to exhibit with excellent gate control and electrical performances. The atomic layer deposited Hf-doped In2O3 thin film transistor annealed at 250 °C exhibits optimal electrical properties, with a field-effect mobility of 18.65 cm2 V-1 s-1, a subthreshold swing of 0.18 V/dec, and an Ion/Ioff ratio of 2.76 × 106. The results indicate that the impact of varying annealing temperatures can be attributed to the modulation of oxygen vacancies within the films. This work serves as a complementary study for the existing post-treatment of oxide films and provides a reliable reference for utilization of the annealing process in practical applications.
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Affiliation(s)
- Jiyuan Zhu
- School of Microelectronics, Fudan University, Shanghai 200433, China
| | - Shen Hu
- School of Microelectronics, Fudan University, Shanghai 200433, China
- Jiashan Fudan Institute, Jiashan 314100, China
| | - Bojia Chen
- School of Microelectronics, Fudan University, Shanghai 200433, China
| | - Shice Wei
- School of Microelectronics, Fudan University, Shanghai 200433, China
| | - Yu Zhang
- School of Microelectronics, Fudan University, Shanghai 200433, China
| | - Xuefeng Wu
- Shanghai Integrated Circuit Manufacturing Innovation Center Co., Ltd., Shanghai 201203, China
| | - Xingli Zou
- State Key Laboratory of Advanced Special Steel, Shanghai Key Laboratory of Advanced Ferrometallurgy, and School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
| | - Xionggang Lu
- State Key Laboratory of Advanced Special Steel, Shanghai Key Laboratory of Advanced Ferrometallurgy, and School of Materials Science and Engineering, Shanghai University, Shanghai 200444, China
| | - Qingqing Sun
- School of Microelectronics, Fudan University, Shanghai 200433, China
| | - David W Zhang
- School of Microelectronics, Fudan University, Shanghai 200433, China
| | - Li Ji
- School of Microelectronics, Fudan University, Shanghai 200433, China
- Jiashan Fudan Institute, Jiashan 314100, China
- Hubei Yangtz Memory Laboratories, Wuhan 430205, China
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Yan X, Hu X, Zhou R, Gao N, Yao Y, Gao Y, Kang J. Enhanced light extraction efficiency of GaN-based green micro-LED modulating by a thickness-tunable SiO 2 passivation structure. OPTICS EXPRESS 2023; 31:39717-39726. [PMID: 38041287 DOI: 10.1364/oe.506590] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2023] [Accepted: 10/25/2023] [Indexed: 12/03/2023]
Abstract
Green micro-light emitting diodes (micro-LEDs) is one of the three primary color light sources as full-color display, which serves as a key research object in the field of micro-LED display. As the micro-LED size decreases, the surface-area-to-volume ratio of the device increases, leading to more serious damage on the sidewall by inductively coupled plasma (ICP) etching. The passivation process of SiO2 provides an effective method to reduce sidewall damage caused by ICP etching. In this work, green rectangular micro-LEDs with passivation layer thickness of 0∼600 nm was designed using the finite-difference time-domain (FDTD) simulation. In order to verify the simulation results, the micro-LED array was fabricated by parallel laser micro-lens array (MLA) lithography in high speed and large area. The effect of the SiO2 passivation layer thickness on the performance of the green micro-LED was analyzed, which shows that the passivation layer thickness-light extraction efficiency curve fluctuates periodically. For the sample with 90 nm thickness of SiO2 passivation layer, there exists a small leakage current and higher operating current density, and the maximum external quantum efficiency (EQE) is 2.8 times higher than micro-LED without SiO2 passivation layer.
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Zhang Y, Xu R, Kang Q, Zhang X, Zhang ZH. Recent Advances on GaN-Based Micro-LEDs. MICROMACHINES 2023; 14:mi14050991. [PMID: 37241615 DOI: 10.3390/mi14050991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 04/29/2023] [Accepted: 04/29/2023] [Indexed: 05/28/2023]
Abstract
GaN-based micro-size light-emitting diodes (µLEDs) have a variety of attractive and distinctive advantages for display, visible-light communication (VLC), and other novel applications. The smaller size of LEDs affords them the benefits of enhanced current expansion, fewer self-heating effects, and higher current density bearing capacity. Low external quantum efficiency (EQE) resulting from non-radiative recombination and quantum confined stark effect (QCSE) is a serious barrier for application of µLEDs. In this work, the reasons for the poor EQE of µLEDs are reviewed, as are the optimization techniques for improving the EQE of µLEDs.
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Affiliation(s)
- Youwei Zhang
- Guangdong Provincial Key Laboratory of Information Photonics Technology, School of Physics and Opto-Electronic Engineering, Guangdong University of Technology, Guangzhou 510006, China
| | - Ruiqiang Xu
- Guangdong Provincial Key Laboratory of Information Photonics Technology, School of Physics and Opto-Electronic Engineering, Guangdong University of Technology, Guangzhou 510006, China
| | - Qiushi Kang
- School of Integrated Circuits, Guangdong University of Technology, Guangzhou 510006, China
| | - Xiaoli Zhang
- Guangdong Provincial Key Laboratory of Information Photonics Technology, School of Physics and Opto-Electronic Engineering, Guangdong University of Technology, Guangzhou 510006, China
| | - Zi-Hui Zhang
- School of Integrated Circuits, Guangdong University of Technology, Guangzhou 510006, China
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