Evidence for multiple impurity bands in sodium-doped silicon MOSFETs

TL;DR

This study investigates sodium-doped silicon MOSFETs, revealing evidence for multiple impurity bands and a soft gap at low temperatures through temperature-dependent conductivity measurements.

Contribution

It provides experimental evidence for multiple impurity bands in sodium-doped silicon MOSFETs and analyzes their electronic density of states.

Findings

Presence of two distinct impurity bands

Existence of a soft gap at low temperature

Screening effects influence conductivity variation

Abstract

We report measurements of the temperature-dependent conductivity in a silicon metal-oxide-semiconductor field-effect transistor that contains sodium impurities in the oxide layer. We explain the variation of conductivity in terms of Coulomb interactions that are partially screened by the proximity of the metal gate. The study of the conductivity exponential prefactor and the localization length as a function of gate voltage have allowed us to determine the electronic density of states and has provided arguments for the presence of two distinct bands and a soft gap at low temperature.