Characterization of As-Grown and Regrown GaN-on-GaN Structures for Vertical p-n Power Devices

This work has investigated the effects of etching treatment on as-grown and regrown GaN-on-GaN structures intended for vertical p-n power device applications. Surfaces of thick unintentionally doped (UID) GaN layers, grown homoepitaxially via metal-organic chemical vapor deposition on freestanding GaN bulk substrates, were subjected to RF-plasma dry etching, and additional layers of UID-GaN/p-GaN were then grown. The as-grown and regrown structures were examined in cross section using transmission electron microscopy. Two different types of etching treatment were used, fast-etch-only and multiple etches with decreasing power. Images of the fast-etch-only devices clearly showed the GaN-on-GaN interface at the etched location, and low device breakdown voltages were measured (reverse bias in the range of 45-95V). In comparison, no interfaces were visible in devices after multiple etching steps, and the corresponding device breakdown voltages were markedly higher (reverse bias similar to 1200-1270V). These results emphasize the importance of optimizing surface etching techniques for avoiding degraded performance in GaN-on-GaN power devices that require GaN regrowth.