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Sarkar M, Adams F, Dar SA, Penn J, Ji Y, Gundimeda A, Zhu T, Liu C, Hirshy H, Massabuau FCP, O'Hanlon T, Kappers MJ, Ghosh S, Kusch G, Oliver RA. Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons. Microsc Microanal 2024; 30:208-225. [PMID: 38578956 DOI: 10.1093/mam/ozae028] [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] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 02/09/2024] [Accepted: 03/04/2024] [Indexed: 04/07/2024]
Abstract
In this article, porous GaN distributed Bragg reflectors (DBRs) were fabricated by epitaxy of undoped/doped multilayers followed by electrochemical etching. We present backscattered electron scanning electron microscopy (BSE-SEM) for sub-surface plan-view imaging, enabling efficient, non-destructive pore morphology characterization. In mesoporous GaN DBRs, BSE-SEM images the same branching pores and Voronoi-like domains as scanning transmission electron microscopy. In microporous GaN DBRs, micrographs were dominated by first porous layer features (45 nm to 108 nm sub-surface) with diffuse second layer (153 nm to 216 nm sub-surface) contributions. The optimum primary electron landing energy (LE) for image contrast and spatial resolution in a Zeiss GeminiSEM 300 was approximately 20 keV. BSE-SEM detects porosity ca. 295 nm sub-surface in an overgrown porous GaN DBR, yielding low contrast that is still first porous layer dominated. Imaging through a ca. 190 nm GaN cap improves contrast. We derived image contrast, spatial resolution, and information depth expectations from semi-empirical expressions. These theoretical studies echo our experiments as image contrast and spatial resolution can improve with higher LE, plateauing towards 30 keV. BSE-SEM is predicted to be dominated by the uppermost porous layer's uppermost region, congruent with experimental analysis. Most pertinently, information depth increases with LE, as observed.
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Affiliation(s)
- Maruf Sarkar
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
| | - Francesca Adams
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
| | - Sidra A Dar
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
| | - Jordan Penn
- Department of Physics, University of Oxford, Oxford OX1 3PJ, UK
| | - Yihong Ji
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
| | - Abhiram Gundimeda
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
| | | | | | | | | | - Thomas O'Hanlon
- Plymouth Electron Microscopy Center, University of Plymouth, Plymouth PL4 8AA, UK
| | - Menno J Kappers
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
| | - Saptarsi Ghosh
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
| | - Gunnar Kusch
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
| | - Rachel A Oliver
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 0FS, UK
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Xu R, Kang Q, Zhang Y, Zhang X, Zhang Z. Research Progress of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes. Micromachines (Basel) 2023; 14:844. [PMID: 37421078 DOI: 10.3390/mi14040844] [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: 03/14/2023] [Revised: 03/31/2023] [Accepted: 04/06/2023] [Indexed: 07/09/2023]
Abstract
AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) have great application prospects in sterilization, UV phototherapy, biological monitoring and other aspects. Due to their advantages of energy conservation, environmental protection and easy miniaturization realization, they have garnered much interest and been widely researched. However, compared with InGaN-based blue LEDs, the efficiency of AlGaN-based DUV LEDs is still very low. This paper first introduces the research background of DUV LEDs. Then, various methods to improve the efficiency of DUV LED devices are summarized from three aspects: internal quantum efficiency (IQE), light extraction efficiency (LEE) and wall-plug efficiency (WPE). Finally, the future development of efficient AlGaN-based DUV LEDs is proposed.
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Affiliation(s)
- 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
| | - Youwei Zhang
- Guangdong Provincial Key Laboratory of Information Photonics Technology, School of Physics and Opto-Electronic Engineering, 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
| | - Zihui Zhang
- School of Integrated Circuits, Guangdong University of Technology, Guangzhou 510006, China
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Zhao Y, Shan M, Zheng Z, Jian P, Liu W, Tan S, Chen C, Wu F, Dai J. Fabrication of wafer-scale nanoporous AlGaN-based deep ultraviolet distributed Bragg reflectors via one-step selective wet etching. Sci Rep 2022; 12:22434. [PMID: 36575216 DOI: 10.1038/s41598-022-25712-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2022] [Accepted: 12/05/2022] [Indexed: 12/29/2022] Open
Abstract
In this paper, we reported on wafer-scale nanoporous (NP) AlGaN-based deep ultraviolet (DUV) distributed Bragg reflectors (DBRs) with 95% reflectivity at 280 nm, using epitaxial periodically stacked n-Al0.62Ga0.38N/u-Al0.62Ga0.38N structures grown on AlN/sapphire templates via metal-organic chemical vapor deposition (MOCVD). The DBRs were fabricated by a simple one-step selective wet etching in heated KOH aqueous solution. To study the influence of the temperature of KOH electrolyte on the nanopores formation, the amount of charge consumed during etching process was counted, and the surface and cross-sectional morphology of DBRs were characterized by Scanning electron microscopy (SEM) and atomic force microscopy (AFM). As the electrolyte temperature increased, the nanopores became larger while the amount of charge reduced, which revealed that the etching process was a combination of electrochemical and chemical etching. The triangular nanopores and hexagonal pits further confirmed the chemical etching processes. Our work demonstrated a simple wet etching to fabricate high reflective DBRs, which would be useful for AlGaN based DUV devices with microcavity structures.
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