Strongly metallic electron and hole 2D transport in an ambipolar Si-vacuum field effect transistor

TL;DR

This study demonstrates strong metallic 2D electron and hole transport in an ambipolar Si-vacuum FET, with theoretical analysis attributing metallicity to temperature-dependent Coulomb disorder screening.

Contribution

It provides the first combined experimental and theoretical analysis of ambipolar 2D transport in a Si-vacuum FET, highlighting the role of Coulomb disorder screening.

Findings

Electron mobility is about 20 times higher than hole mobility.

Both electrons and holes show metallic temperature dependence in conductivity.

Theory based on RPA screening explains the observed metallic behavior.

Abstract

We report experiment and theory on an ambipolar gate-controlled Si-vacuum field effect transistor (FET) where we study electron and hole (low-temperature 2D) transport in the same device simply by changing the external gate voltage to tune the system from being a 2D electron system at positive gate voltage to a 2D hole system at negative gate voltage. The electron (hole) conductivity manifests strong (moderate) metallic temperature dependence with the conductivity decreasing by a factor of 8 (2) between 0.3 K and 4.2 K with the peak electron mobility ($\sim 18$ m$^2$/Vs) being roughly 20 times larger than the peak hole mobility (in the same sample). Our theory explains the data well using RPA screening of background Coulomb disorder, establishing that the observed metallicity is a direct consequence of the strong temperature dependence of the effective screened disorder.