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A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors

Ben Thornley Orcid Logo, Maruf Sarkar Orcid Logo, Saptarsi Ghosh Orcid Logo, Martin Frentrup, Menno J. Kappers, Thom R. Harris-Lee, Rachel A. Oliver Orcid Logo

Acta Materialia, Volume: 308, Start page: 121957

Swansea University Author: Saptarsi Ghosh Orcid Logo

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DOI (Published version): 10.1016/j.actamat.2026.121957

Abstract

Fabrication of porous GaN distributed Bragg reflectors (DBRs) via the selective electrochemical etching of conductive Si-doped layers, separated by non-intentionally doped (NID) layers, provides a straightforward methodology for producing highly reflective DBRs suitable for device overgrowth and int...

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Published in: Acta Materialia
ISSN: 1359-6454
Published: Elsevier BV 2026
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Such photonic materials can be fabricated by a lithography-free defect-driven etching process, where threading dislocations intrinsic to heteroepitaxy form nanoscale channels that facilitate etchant transport through NID layers. Here, we report the first three-dimensional characterisation of porous GaN-on-Si DBRs fabricated in this methodology with different etching voltages, using serial-section tomography in a focused ion beam scanning electron microscope (FIB-SEM). These datasets reconstruct the pore morphology as etching proliferates through the alternating Si-doped/NID layer stack. Volumetric reconstruction enabled us to enhance the established &#x2018;kebab&#x2019; model for defect-driven etching by proposing a &#x2018;cascade&#x2019; model where the etchant cascades through the material via vertical etching down nanopipes and horizontal etching across pores, forming complex networks directly related to the pathways taken. 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spelling 2026-04-10T13:55:18.1873487 v2 71576 2026-03-07 A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors 3e247ecabd6eddd319264d066b0ce959 0000-0003-1685-6228 Saptarsi Ghosh Saptarsi Ghosh true false 2026-03-07 ACEM Fabrication of porous GaN distributed Bragg reflectors (DBRs) via the selective electrochemical etching of conductive Si-doped layers, separated by non-intentionally doped (NID) layers, provides a straightforward methodology for producing highly reflective DBRs suitable for device overgrowth and integration, which has otherwise proven difficult in the III-nitride epitaxial system via conventional alloying. Such photonic materials can be fabricated by a lithography-free defect-driven etching process, where threading dislocations intrinsic to heteroepitaxy form nanoscale channels that facilitate etchant transport through NID layers. Here, we report the first three-dimensional characterisation of porous GaN-on-Si DBRs fabricated in this methodology with different etching voltages, using serial-section tomography in a focused ion beam scanning electron microscope (FIB-SEM). These datasets reconstruct the pore morphology as etching proliferates through the alternating Si-doped/NID layer stack. Volumetric reconstruction enabled us to enhance the established ‘kebab’ model for defect-driven etching by proposing a ‘cascade’ model where the etchant cascades through the material via vertical etching down nanopipes and horizontal etching across pores, forming complex networks directly related to the pathways taken. This accounts for premature nanopipe termination and discontinuities in nanopipe formation, where dislocations are observed to activate and deactivate individually. Statistical analysis of individual etching behaviour, across all dislocations for each tomograph, revealed a greater tendency to form continuous structures that follow conventional ‘kebab’ behaviour at higher etching voltages. We propose that higher etching voltages alter the probability of dislocation etching relative to doped layer etching, thereby empowering morphological optimisation through improved mechanistic understanding of electrochemical etching. Journal Article Acta Materialia 308 121957 Elsevier BV 1359-6454 Nanoporous; Nitrides; Tomography; Dislocations; Distributed Bragg reflectors 15 4 2026 2026-04-15 10.1016/j.actamat.2026.121957 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 Ernest Oppenheimer Trust at the University of Cambridge and by the Royal Academy of Engineering under the Chairs in Emerging Technologies scheme, funded by the Department for Science, Innovation and Technology (DSIT). We acknowledge the support of the Wolfson Electron Microscopy Suite and the use of the Zeiss Crossbeam 540 funded by Royce under grant EP/R008779/1. The EPSRC also supported this research under Grant Nos. EP/R03480X/1, EP/W03557X/1, EP/X015300/1, EP/N509620/1, and EP/R513180/1 as well as under Project Reference 2278538. We also acknowledge funding from The Armourers and Brasiers’ Gauntlet Trust. 2026-04-10T13:55:18.1873487 2026-03-07T16:08:49.0472827 Faculty of Science and Engineering School of Aerospace, Civil, Electrical, General and Mechanical Engineering - Electronic and Electrical Engineering Ben Thornley 0009-0009-5475-3917 1 Maruf Sarkar 0000-0001-6156-5089 2 Saptarsi Ghosh 0000-0003-1685-6228 3 Martin Frentrup 4 Menno J. Kappers 5 Thom R. Harris-Lee 6 Rachel A. Oliver 0000-0003-0029-3993 7 71576__36492__f66b43fd11634d7aaf914778483b2863.pdf 71576.VoR.pdf 2026-04-10T13:52:53.9121256 Output 7052764 application/pdf Version of Record true © 2026 The Authors. This is an open access article under the CC BY license. true eng http://creativecommons.org/licenses/by/4.0/
title A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
spellingShingle A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
Saptarsi Ghosh
title_short A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
title_full A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
title_fullStr A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
title_full_unstemmed A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
title_sort A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
author_id_str_mv 3e247ecabd6eddd319264d066b0ce959
author_id_fullname_str_mv 3e247ecabd6eddd319264d066b0ce959_***_Saptarsi Ghosh
author Saptarsi Ghosh
author2 Ben Thornley
Maruf Sarkar
Saptarsi Ghosh
Martin Frentrup
Menno J. Kappers
Thom R. Harris-Lee
Rachel A. Oliver
format Journal article
container_title Acta Materialia
container_volume 308
container_start_page 121957
publishDate 2026
institution Swansea University
issn 1359-6454
doi_str_mv 10.1016/j.actamat.2026.121957
publisher Elsevier BV
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 Fabrication of porous GaN distributed Bragg reflectors (DBRs) via the selective electrochemical etching of conductive Si-doped layers, separated by non-intentionally doped (NID) layers, provides a straightforward methodology for producing highly reflective DBRs suitable for device overgrowth and integration, which has otherwise proven difficult in the III-nitride epitaxial system via conventional alloying. Such photonic materials can be fabricated by a lithography-free defect-driven etching process, where threading dislocations intrinsic to heteroepitaxy form nanoscale channels that facilitate etchant transport through NID layers. Here, we report the first three-dimensional characterisation of porous GaN-on-Si DBRs fabricated in this methodology with different etching voltages, using serial-section tomography in a focused ion beam scanning electron microscope (FIB-SEM). These datasets reconstruct the pore morphology as etching proliferates through the alternating Si-doped/NID layer stack. Volumetric reconstruction enabled us to enhance the established ‘kebab’ model for defect-driven etching by proposing a ‘cascade’ model where the etchant cascades through the material via vertical etching down nanopipes and horizontal etching across pores, forming complex networks directly related to the pathways taken. This accounts for premature nanopipe termination and discontinuities in nanopipe formation, where dislocations are observed to activate and deactivate individually. Statistical analysis of individual etching behaviour, across all dislocations for each tomograph, revealed a greater tendency to form continuous structures that follow conventional ‘kebab’ behaviour at higher etching voltages. We propose that higher etching voltages alter the probability of dislocation etching relative to doped layer etching, thereby empowering morphological optimisation through improved mechanistic understanding of electrochemical etching.
published_date 2026-04-15T05:51:55Z
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score 11.101457

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