Effects of a thin Al layer insertion between AlGaN and Schottky gate on the AlGaN∕GaN high electron mobility transistor characteristics

To improve an AlGaN∕GaN high electron mobility transistor, an Al layer as thin as 3 nm was inserted between the AlGaN barrier layer and the gate contact. At our preceded experiments on Schottky diodes, we confirmed significant improvement in capacitance-gate voltage characteristics especially at a low frequency as well as drastic reduction in gate leakage current, which should be interpreted in terms of decrease in oxygen-related trap density at the AlGaN surface. As a result of the trap reduction, the transistor indicates marked improvement of current collapse with no degradation in transconductance.