Dual Operation Modes of the Ge Schottky Barrier Metal-Oxide-Semiconductor Field-Effect Transistor

Detectors and computers, especially those which exploit quantum phenomena, often operate at low temperatures. Such systems may include circuits based on germanium, a conventional semiconductor that has found new applications.  Often, the signals generated at the coldest stages are weak. Transmission of the weak signal to warmer temperatures adds noise which further reduces the signal-to-noise ratio, making detection challenging and increasing the bit error rate. Therefore, it is beneficial to amplify the signal at the coldest stage of the instrument, where the noise is minimized. If the signal of interest is generated by a cryogenic circuit that lies on top of a semiconductor substrate, an amplifier could be monolithically integrated with the rest of the circuit for a compact footprint. To date, signal amplification in germanium-based circuits has not been thoroughly investigated.

Here, a germanium p-channel metal oxide semiconductor field effect transistor (MOSFET), with germanium-metal Schottky contacts, is experimentally demonstrated at a temperature of 4 Kelvin towards the goal of a monolithically integrated amplifier. The p-channel MOSFET turns on at a gate voltage of ‑1.6 V and shows a peak mobility of 500 cm²/Vs at carrier density 3 x 10¹² cm^‑2. At high drain-source bias voltages, the device operates in a non-conventional mode where the current is limited by the source contact and is gate controllable. In this mode, the transconductance is greater than the theoretical value for a conventional MOSFET with the same geometry, mobility, and capacitance. The fabrication process has a low thermal budget and requires neither doping nor ion implantation, making it suitable for monolithic integration.

 

This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. DOE, Office of Basic Energy Sciences user facility. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. The views expressed here do not necessarily represent the views of the DOE or the U.S. Government.