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 ~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.