High-selectivity dry etching for p-type GaN gate formation of normally-off operation high-electron-mobility transistor

Selective dry etching of GaN to AlGaN was studied to form a p-type GaN gate on an AlGaN/GaN high-electron-mobility transistor (HEMT). The epitaxial layer consists of Mg-doped GaN, 15 nm thick Al0.25GaN, GaN channel, and buffer layers on a Si substrate. The inductively coupled plasma (ICP) etching technique was employed with the ICP and bias powers of 120 and 7 W, respectively, using Cl2 and Ar gases with flow rates of 20 and 5 sccm, respectively. Then, the O2 addition effects were investigated for the etching of GaN and AlGaN by changing the O2 flow rate. At the rate of 1 sccm, the etching rate ratio of GaN to AlGaN was found to be about 50 with a smooth surface. Using the etching condition obtained, the p-GaN gate HEMT with the positive threshold voltage of 1.2 V and high drain current of 440 mA mm−1 was successfully fabricated.