The AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) with ZnO gate insulator deposited using a vapor cooling condensation system were fabricated. The AlGaN surface treatment using (NH4) 2Sx was performed to improve the quality of the interface between the ZnO layer and AlGaN layer. The (NH4)2S x-treated MOS-HEMTs exhibited a higher saturation drain-source current of 0.74 A/mm, a maximum extrinsic transconductance of 200 mS/mm, an unit gain cutoff frequency of 9.1 GHz, a maximum frequency of oscillation of 17.1 GHz, and the Hooge's coefficient of 8.28× 10-6. The improved performances of the (NH4)2Sx-treated MOS-HEMTs were attributed to the reduction in surface states.
All Science Journal Classification (ASJC) codes