Doped Barrier Al0.6Ga0.35N/Al0.40Ga0.60N MOSHFET With SiO2 Gate-Insulator and Zr-Based Ohmic Contacts

This letter reports an Al0.6Ga0.35N-Al0.40Ga0.60N metal-oxide-semiconductor-heterojunction-field-effect-transistor (MOSHFET) with an SiO2 gate-insulator. For this first demonstration of an AlGaN channel MOSHFET, a new doped barrier epilayer design led to linear source-drain ohmic-contacts formed by Zr-based metal stack with a contact resistance as low as 1.64 Omega.mm. For a device with 6-mu m source-drain opening a record saturation current of 0.6 A/mm (at gate bias of 6V) was measured. In contrast to a conventional Schottky-gate HFET, the gate-oxide from the pulsed plasma enhanced chemical vapor deposition decreased the MOSHFET gate leakage current by a factor of 10(4) with only a 1.5-V shift in the threshold voltage. A drift mobility of 430 cm(2)/V.s is measured at zero-gate bias, which increases to 800 cm(2)/V.s close to the threshold voltage. The device characteristics up to 250 degrees C are used to calculate the temperature dependence of the drift mobility.