Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons

Sarkar, Maruf; Adams, Francesca; Dar, Sidra A; Penn, Jordan; Ji, Yihong; Gundimeda, Abhiram; Zhu, Tongtong; Liu, Chaowang; Hirshy, Hassan; P, Fabien C; O’Hanlon, Thomas; Kappers, Menno J; Ghosh, Saptarsi; Kusch, Gunnar; Oliver, Rachel A

doi:10.1093/mam/ozae028

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Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons

Maruf Sarkar

, Francesca Adams

, Sidra A Dar

, Jordan Penn

, Yihong Ji

, Abhiram Gundimeda

, Tongtong Zhu

, Chaowang Liu, Hassan Hirshy

, Fabien C P Massabuau

, Thomas O’Hanlon

, Menno J Kappers

, Saptarsi Ghosh

, Gunnar Kusch

, Rachel A Oliver

Microscopy and Microanalysis, Volume: 30, Issue: 2, Pages: 208 - 225

Swansea University Author: Saptarsi Ghosh

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DOI (Published version): 10.1093/mam/ozae028

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...

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Published in:	Microscopy and Microanalysis
ISSN:	1431-9276 1435-8115
Published:	Oxford University Press (OUP) 2024
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URI:	https://cronfa.swan.ac.uk/Record/cronfa66865
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spelling	v2 66865 2024-06-23 Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons 3e247ecabd6eddd319264d066b0ce959 0000-0003-1685-6228 Saptarsi Ghosh Saptarsi Ghosh true false 2024-06-23 ACEM 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. Journal Article Microscopy and Microanalysis 30 2 208 225 Oxford University Press (OUP) 1431-9276 1435-8115 backscattered electrons (BSEs), distributed Bragg reflectors (DBRs), porous gallium nitride, scanning electron microscopy (SEM), sub-surface imaging 29 4 2024 2024-04-29 10.1093/mam/ozae028 COLLEGE NANME Aerospace, Civil, Electrical, and Mechanical Engineering COLLEGE CODE ACEM Swansea University Another institution paid the OA fee This work was supported by the UK under Grant Nos. EP/N509620/1, EP/R513180/1, and EP/R03480X/1. Maruf Sarkar would also like to acknowledge funding from The Armourers and Brasiers’ Gauntlet Trust. Rachel Oliver would like to acknowledge funding from the Royal Academy of Engineering under the Chairs in Emerging Technologies Scheme, which is sponsored by the Department for Science, Innovation and Technology (DSIT). 2024-07-03T16:01:06.2320141 2024-06-23T19:48:41.6509014 Faculty of Science and Engineering School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Electronic and Electrical Engineering Maruf Sarkar 0000-0001-6156-5089 1 Francesca Adams 0009-0008-2033-2121 2 Sidra A Dar 0000-0002-5048-6147 3 Jordan Penn 0009-0002-3572-1724 4 Yihong Ji 0009-0000-5147-3447 5 Abhiram Gundimeda 0000-0001-5208-1920 6 Tongtong Zhu 0000-0002-9481-8203 7 Chaowang Liu 8 Hassan Hirshy 0000-0003-0281-3681 9 Fabien C P Massabuau 0000-0003-1008-1652 10 Thomas O’Hanlon 0000-0002-4700-7141 11 Menno J Kappers 0000-0002-6566-0742 12 Saptarsi Ghosh 0000-0003-1685-6228 13 Gunnar Kusch 0000-0003-2743-1022 14 Rachel A Oliver 0000-0003-0029-3993 15 66865__30805__d2c2ca2993b44150bde6fecbf5491cc7.pdf 66865.VoR.pdf 2024-07-03T15:59:43.0912768 Output 2150000 application/pdf Version of Record true © The Author(s) 2024. This is an Open Access article distributed under the terms of the Creative Commons Attribution License. true eng https://creativecommons.org/licenses/by/4.0/
title	Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons
spellingShingle	Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons Saptarsi Ghosh
title_short	Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons
title_full	Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons
title_fullStr	Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons
title_full_unstemmed	Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons
title_sort	Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons
author_id_str_mv	3e247ecabd6eddd319264d066b0ce959
author_id_fullname_str_mv	3e247ecabd6eddd319264d066b0ce959_***_Saptarsi Ghosh
author	Saptarsi Ghosh
author2	Maruf Sarkar Francesca Adams Sidra A Dar Jordan Penn Yihong Ji Abhiram Gundimeda Tongtong Zhu Chaowang Liu Hassan Hirshy Fabien C P Massabuau Thomas O’Hanlon Menno J Kappers Saptarsi Ghosh Gunnar Kusch Rachel A Oliver
format	Journal article
container_title	Microscopy and Microanalysis
container_volume	30
container_issue	2
container_start_page	208
publishDate	2024
institution	Swansea University
issn	1431-9276 1435-8115
doi_str_mv	10.1093/mam/ozae028
publisher	Oxford University Press (OUP)
college_str	Faculty of Science and Engineering
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hierarchy_top_id	facultyofscienceandengineering
hierarchy_top_title	Faculty of Science and Engineering
hierarchy_parent_id	facultyofscienceandengineering
hierarchy_parent_title	Faculty of Science and Engineering
department_str	School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Electronic and Electrical Engineering{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Electronic and Electrical Engineering
document_store_str	1
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description	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.
published_date	2024-04-29T16:01:04Z
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score	11.01438

Sub-surface Imaging of Porous GaN Distributed Bragg Reflectors via Backscattered Electrons

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