Normally-off AlGaN/GaN MIS-HEMTs with high 2DEG mobility enabled by shallow recess and oxygen plasma treatment

We demonstrate a normally-off operation in Al2O3/AlGaN/GaN MIS-HEMTs with a high two-dimensional electron gas (2DEG) mobility enabled by a shallow recess channel structure and oxygen plasma treatment. In the channel region, the original 25-nm-thick AlGaN barrier layer was thinned down to 9 nm, which in principle, should yield a normally-on operation. However, we show that a pre-insulator deposition oxygen plasma treatment shifts the threshold voltage to +1.4 V. The relatively thick AlGaN barrier facilitated a minimal sacrifice of channel 2DEG mobility retaining a value as high as 1800 cm2V-1s-1, resulting in a high drain current of 600 mA mm-1.