(Invited) Selective Area Etching and Doping of GaN for High-Power Applications

Abstract

Selective-area doping techniques of GaN have been studied intensively for high-power applications. Diffusion or implantation of dopants is a very mature approach in Si and SiC, but it is still under investigation for GaN. Selective area epitaxy and doping is an alternative method to overcome the barrier and is reported by many groups. Two aspects will be discussed, including selective-area etching and non-uniform Mg doping in non-planar regrown trenches.Dry etching has been commonly applied to create high-aspect ratio and smooth trenches, but has also been reported to generate serious optical and electronic defects and impurities on the treated surface. Here, we report using an in-situ etchant, tertiarybutylchloride (TBCl), to replace the dry etching process. In order to demonstrate the effectiveness of TBCl etching, planar PN diodes were grown and fabricated, including continuous, dry-etched, and TBCl-etched and regrown ones. TBCl-etched and regrown device demonstrates electrical properties approach that of the continuous grown diode in the forward and reverse biased conditions.On the other hand, non-uniform doping of Mg was observed in the non-planar regrowth by several groups. With nanoscale characterization technique, atom probe tomography (APT), we identified the origin of the non-uniformity. The Mg concentration is approximately inversely proportional to the growth rate beginning ~20 nm from the regrowth interface. It indicates that the existence of semi-polar facets together with the anisotropy in the growth rate are the origin of non-uniformity. Furthermore, the evolving shape of semi-polar facets could be explained by the kinetic Wulff theorem.