Depletion-mode In0.2Ga0.8As/GaAs MOSFET with molecular beam epitaxy grown Al2O3/Ga2O3(Gd2O3) as gate dielectrics

Depletion-mode In0.2Ga0.8As/GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated with molecular beam epitaxy (MBE) grown Al2O3/Ga2O3(Gd2O3) as the gate dielectric in two comparable processes. In the 'metal-gate-last' process, a 12 mum gate-length depletion-mode n-channel InGaAs/GaAs MOSFET with a Ga2O3(Gd2O3) gate oxide 6 nm thick shows an accumulated drain current density of 135 mA/mm at Vg=2 V. In the other process of 'metal-gate-first' process, the device with same gate dielectric, channel, and gate length exhibits a larger drain current density of 175 mA/mm at the same gate bias. In addition, there is a broader transfer characteristics and higher extrinsic peak transconductance of 48 mS/mm in the metal-gate-first process. MOS capacitors from both processes have exhibited excellent capacitance-voltage (C-V) characteristics with minor dispersion, negligible hysteresis, and kappa values of 13.7-13.9 in Ga2O3(Gd2O3).