Implementation of Recessed Gate Normally off GaN Metal–Insulator–Semiconductor High Electron Mobility Transistors by Electrodeless Photoelectrochemical Etching

We demonstrated that electrodeless photoelectrochemical (ELPEC) etching can be used to realize recessed gate normally off GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs). A slower speed etching of 0.36 nm/min has been achieved by the ELPEC etching, and it was easy to control the etching depth at this etching rate. The normally off GaN MISHEMT has been fabricated with a 20 nm atomic layer deposition hafnium oxide (HfO2) gate dielectric after a 55 min ELPEC etching, and low etched surface roughness has been obtained. A threshold voltage shift from −3.6 to 0.5 V has been achieved, performing with normally off properties. A maximum output current of 500 mA/mm and a high maximum field-effect mobility of 194 cm2/V·s has been obtained due to the high quality etching surface created with ELPEC etching.