High Temperature and High Frequency Characteristics of AlGaN/GaN MOS-HFETs with Photochemical Vapor Deposited SiO2 Layer

High quality SiO2 film was successfully deposited onto AlGaN as a dielectric layer for our AlGaN/GaN MOS-HFETs using the photochemical vapor deposition (photo-CVD) technique, with D2 lamp as the excitation source. By comparing with other conventional AlGaN/GaN HFETs with similar structures, we found out that the gate leakage current can be reduced by more than four orders of magnitude, even at elevated temperatures. With vds = 20 V and V8 = -8V (cutoff), the leakage current at room temperature was about 6.46 mA/mm, which is almost identical to that (6.48mA/mm) of measured at 300°C, and most of all, relatively larger Id,max and gm,max could still be achieved when compared to conventional HFETs. In addition, the extrinsic cutoff frequencies fT's for both MOS-HFETs and HFETs were measured to be 4.05 GHz and 3.36 GHz, respectively. Furthermore, the corresponding fmax's for MOS-HFETs and HFETs were also found to be 6.85 GHz and 5.45 GHz, respectively.