Dual operation modes of the Ge Schottky barrier metal-oxide-semiconductor field-effect transistor

A germanium p-channel Schottky barrier metal-oxide-semiconductor field-effect transistor (SB-MOSFET) with germanium-platinum Schottky contacts is demonstrated experimentally. The fabrication process has a low thermal budget of 450 ° C and requires neither intentional doping nor ion implantation. At a temperature of 4 K, the p-channel SB-MOSFET turns on at a gate voltage of −1.6 V and shows a peak mobility of 500 cm²/V s at a carrier density of 3 × 10¹² cm^-2. Under high drain-source bias voltages, the device operates in an unconventional mode where the current is limited by the source contact. Injection of carriers from the source contact to the germanium channel is controlled by the gate bias, which modulates the Schottky barrier capacitively. The transconductance in this mode deviates from and is significantly higher than the value expected for a conventional MOSFET with the same geometry, mobility, and capacitance. Based on four-point current-voltage measurements, we present a theoretical band diagram of the device and give a physical picture for the observed high currents and transconductances.