Surface control of GaN alloys for photonic and electronic devices

Abstract

Surface characterization and control technologies were applied to GaN and AlGaN surfaces. It was found that a unique "air-gap CV" technique is effective in evaluating surface state density on free AlGaN surfaces. A photoelectrochemical process, utilizing a mixed solution of propylene glycol and tartaric acid, was employed to form a thin oxide layer on GaN and AlGaN. We observed an enhancement of drain current in the AlGaN/GaN HEMT having a narrow channel width of 500 nm after the oxidation of the channel walls by the electrochemical process. To improve the uniformity of the effective electric field in the channel, a multi-mesa-channel (MMC) AlGaN/GaN HEMT has been proposed and developed. With forming a periodic trench just under the gate region by an ECR-plasma assisted dry etching, the MMC HEMT has parallel mesa-shaped channels with 2-dimensional electron gas (2DEG) surrounded by the top-and side-gate electrodes.