Electric Field Effect Analysis of Thin PbTe films on high-epsilon SrTiO3 Substrate

TL;DR

This study investigates the electric field effect on thin PbTe films on SrTiO3 substrates, revealing high sensitivity, the ability to map the Fermi level dependence on electric displacement, and that the films have a mobility gap larger than bulk PbTe.

Contribution

The paper introduces a theoretical model for measuring Fermi level dependence on electric displacement in thin PbTe films on high-epsilon SrTiO3 substrates.

Findings

High electric displacement allows detailed EFE resistance and Hall constant measurements.

Fermi level can be shifted across the gap to map in-gap states.

PbTe films exhibit a mobility gap larger than bulk PbTe.

Abstract

Thin PbTe films (thickness 500 - 600 angstrom), deposited on SrTiO3, have been investigated by electric field effect (EFE). The high resistivity of such thin films warrants a high sensitivity of the EFE method. The SrTiO3 substrate serves as the dielectric layer in the Gate-Dielectric-PbTe structure. Due to the large dielectric constant of SrTiO3, particularly at low temperatures, the electric displacement D in the film reaches the high value of about 10^8 V/cm, and the EFE introduced charge into the PbTe film amounts to ~ 8 microC/cm2. The high D permits to measure the EFE resistance and Hall constant over a wide region of D, revealing the characteristic features of their D-dependence. An appropriate theoretical model has been formulated, showing that, for such films, one can measure the dependence of the Fermi level on D. In fact, we demonstrate that shifting the Fermi level across the gap by varying D, the density-of-states of the in-gape states can be mapped out. Our results show, that the PbTe layers studied, possess a mobility gap exceeding the gap of bulk PbTe.