Analysis of In-Situ Electrochemical Characterisation Methods for Porous GaN Distributed Bragg Reflectors

The applicability of porous GaN distributed Bragg reflectors (DBRs) is currently limited by non-uniformity and a lack of electrochemical etching (ECE) control. This work presents a detailed comparison of ex-situ and in-situ characterisation techniques for analysing pore morphology, uniformity, and ECE progression in dislocation-mediated porous DBR fabrication. A double layer capacitance (CDL) protocol has been developed and integrated with ECE as a real-time measurement of pore surface area. Ex-situ methods (cross-sectional SEM, BSE imaging, FIB-SEM tomography) provide valuable structural insight, but each possesses significant limitations, and none provide live insight to the ECE progression. In-situ electrochemical measurements (ECE current, charge, and CDL) are shown to be unable to entirely replace ex-situ analysis due to overlapping contributions from different layers being electrochemically etched simultaneously, but offer complementary information to enhance the process of DBR optimisation and provide real-time pore evolution and morphology data. Combining in-situ and ex-situ characterisation offers an improved understanding of porous GaN DBR formation, providing a foundation for systematic optimisation and improved fabrication of high-performance, scalable porous DBR structures.