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A cascade model for the defect-driven etching of porous GaN distributed Bragg reflectors
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Maruf Sarkar ,
Saptarsi Ghosh ,
Martin Frentrup,
Menno J. Kappers,
Thom R. Harris-Lee,
Rachel A. Oliver
Acta Materialia, Volume: 308, Start page: 121957
Swansea University Author:
Saptarsi Ghosh
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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...
| Published in: | Acta Materialia |
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| ISSN: | 1359-6454 |
| Published: |
Elsevier BV
2026
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| Online Access: |
Check full text
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| URI: | https://cronfa.swan.ac.uk/Record/cronfa71576 |
| 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 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. |
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| Keywords: |
Nanoporous; Nitrides; Tomography; Dislocations; Distributed Bragg reflectors |
| College: |
Faculty of Science and Engineering |
| Funders: |
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. |
| Start Page: |
121957 |