Analysis of <i>in situ</i> electrochemical characterization methods for porous GaN distributed Bragg reflectors

Abstract

The applicability of porous gallium nitride (GaN) distributed Bragg reflectors (DBRs) is currently limited by nonuniformity and a lack of electrochemical etching (ECE) control. This work presents a detailed comparison of ex situ and in situ characterization techniques for analyzing 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 scanning electron microscopy (SEM), backscattered electron imaging, and focused ion beam-SEM tomography] provide valuable structural insight, but each possesses significant limitations, and none provide live insight into 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 optimization and provide real-time pore evolution and morphology data. Combining in situ and ex situ characterization offers an improved understanding of porous GaN DBR formation, providing a foundation for systematic optimization and improved fabrication of high-performance, scalable porous DBR structures.