Depletion-mode InGaAs/GaAs MOSFET with Oxide Passivated by Amorphous Si

It has been shown that a low interface state (Dit) <1011cm-2ev-1 between Ga2O3(Gd2O3) oxide and In0.2Ga0.8As channel using E-beam evaporation in ultra-high-vacuum(UHV) MBE system made MOSFET successfully fabricated. However, any oxide without protection will be damaged during device processing, and the device degrades. In this work, the gate oxides Ga2O3(Gd2O3) are capped with amorphous Si prior to removal from the UHV chamber to avoid moisture and other contaminations. A 1.6 µm-gate-length depletion-mode GaAs MOSFET with In0.2Ga0.8 As/GaAs as channel layers shows a drain current of 370 mA/mm at VG = 0V. Complete pinch-off at VG = -6V and operation in the accumulation mode of up to VG = 2V are measured. The lower transconductance of 70 mS/mm is due to the higher doping concentration and 540Å oxide thickness. However, the transconductance versus gate bias is broader than the best reported data. The device shows hysteresis-free drain current, and high, symmetrical breakdown voltages of 20V.