High temperature and high frequency characteristics of AlGaN/GaN MOS-HFETs with photochemical vapor deposition 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, it was found that the gate leakage current can be reduced by more than four orders of magnitude, even at elevated temperatures. With Vds = 20 V and Vgs= -8 V (cut-off region), the leakage current at room temperature was about 6.46 mA/mm, which is almost identical to that (6.48 mA/mm) of measured at 300 DGC, and most of all, relatively larger I(ds,max) and g(m,max) could still be achieved when compared to conventional HFETs. In addition, the extrinsic cut-off frequencies fT's for both MOS-HFETs and HFETs were measured to be 4.05 GHz and 3.36 GHz, respectively. Furthermore, the corresponding f(max)'s for MOS-HFETs and HFETs were also found to be 6.85 GHz and 5.45 GHz, respectively.