Influence of metal-insulator-semiconductor gate structure on normally-off p-GaN heterojunction field-effect transistors

Abstract

Abstract Normally-off MIS p-GaN HFETs were demonstrated with the self-aligned-gate first (SAG) and the conventional gate (CG) processes. The good ohmic contact with a contact resistance of 1.45 Ω mm was obtained by the low-temperature ohmic technique. By employing the SiO2 as insulator layer, the threshold voltage was enhanced to 2 V and 2.5 V for the SAG and CG devices, respectively. On the other hand, the CG device presented a higher channel resistance than the SAG one. Those phenomenon were interpreted by the different gate structures of two kinds of devices. It demonstrated that the SAG structure was more advanced to achieve good performance in normally-off MIS HFETs with p-GaN cap layer.