Selective etching of p-GaN over Al0.25Ga0.75N in Cl2/Ar/O2 ICP plasma for fabrication of normally-off GaN HEMTs

Abstract

The article presents the results of development of selective etching of p-GaN over Al0.25Ga0.75N in Cl2/Ar/O2 ICP plasma for fabrication of normally-off p-GaN gate GaN HEMTs using a laser reflectometry system for precise control of the etched material thickness. By optimizing etching process parameters such as oxygen flow, ICP power and chamber pressure, high etching selectivity of p-GaN over Al0.25Ga0.75N were obtained, with values up to 56:1. High etching selectivity and the control of etch rates of p-GaN and Al0.25Ga0.75N layers withing a wide range by changing the ICP process parameters enabled application of developed etching processes in the technology of fabrication of normally-off AlGaN/GaN HEMTs with a p-GaN gate. High threshold voltage of around 1.6 V and current densities up to 400 mA/mm were obtained. Electrical measurements have shown that the shortest 1 min Al0.25Ga0.75N overetch time after selective etching of the p-GaN layer results in best electrical parameters of fabricated devices.