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

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

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

Swansea University Author: Saptarsi Ghosh Orcid Logo

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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
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa66865
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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.
Keywords: backscattered electrons (BSEs), distributed Bragg reflectors (DBRs), porous gallium nitride, scanning electron microscopy (SEM), sub-surface imaging
College: Faculty of Science and Engineering
Funders: 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).
Issue: 2
Start Page: 208
End Page: 225