Neutral beam etching for device isolation in AlGaN/GaN HEMTs

In this article, we report a suppression of leakage current and an improvement of isolation breakdown voltage on GaN-based high electron mobility transistors (HEMTs) by means of neutral beam (NB) etching. The plasma damage during dry etching process is one of the key reasons for an isolation leakage current, gate leakage current, and current collapse in GaN HEMTs. Since NB etching is virtually free from electrical charges and has few UV photons, it is possible to reduce plasma damage on an etched surface and improve device characteristics. In this work, we introduced NB etching to the device isolation process of GaN HEMTs and characterized isolation leakage currents at DC and step-stress bias conditions. We also measured the breakdown voltages on two-terminal test element arrays. We compared the characteristics with samples etched by conventional plasma-like beam (PB) etching. Our results suggest that NB etching reduces the leakage current through the etched surface of the mesa isolation, which results in superior breakdown voltages.