AlGaN/GaN high-electron-mobility transistor with transparent gate by Al-doped ZnO

AlGaN/GaN high electron mobility transistors (HEMTs) with Al-doped ZnO (AZO) transparent gate electrodes are fabricated, and the Ni/Au/Ni-gated HEMTs are produced in comparison. The AZO-gated HEMTs show good DC characteristics and Schottky rectifying characteristics, and the gate electrodes achieve excellent transparencies. Compared with Ni/Au/Ni-gated HEMTs, AZO-gated HEMTs show low saturation current, high threshold voltage, high Schottky barrier height, and low gate reverse leakage current. Due to the higher gate resistivity, AZO-gated HEMT exhibits current-gain cutoff frequency (f_T) of 10 GHz and power gain cutoff frequency (f_max) of 5 GHz, and lower maximum oscillation frequency than Ni/Au/Ni-gated HEMTs. Moreover, the characteristics of C-V are measured, and the gate interface characteristics of the AZO-gated devices are investigated by C-V dual sweep.