Studies on optical analysis and optimized fabrication of self-rolled-up GaN mirotube by photoelectrochemical etching

Abstract

Group III nitride semiconductors have direct and wide bandgap energy including visible region which is useful to make optical devices. Using large lattice constant difference between GaN and AlN in nitride semiconductors, we fabricated microtube resonators by sequential growth using metal-organic chemical vapor deposition and horizontal photoelectrochemical etching. These resonators offer several advantages, such as low-cost fabrication, simple mechanism, and the potential for sensor applications due to their thin wall thickness. In this work, we optimized the fabrication of microtubes and improved the yield. Inspired by the fact that only the region exposed by the laser undergoes etching during photoelectrochemical etching, we employed an optical diffuser to increase the laser size, resulting in a significantly increased etching area. The laser size could be adjusted using an iris, and experimental results indicated that photoelectrochemical etching was successful at laser densities of around 0.1 mW/mm^2 or higher when the InGaN layer was approximately 10 nm thickness. Furthermore, by using an aspect ratio of 1:2, with a higher width side in the pattern, we achieved a higher yield of microtubes rolled-up in the desired width direction, as opposed to the previous randomly rolling direction.