Suppression of bulk conductivity in InAs/GaSb broken gap composite quantum wells

TL;DR

This paper explores methods to suppress bulk conductivity in InAs/GaSb quantum wells by controlling gallium impurity levels, achieving high bulk resistance and maintaining topological insulator properties.

Contribution

It demonstrates that intentional impurity incorporation in gallium sources significantly increases bulk resistance in InAs/GaSb quantum wells, enhancing topological insulator behavior.

Findings

Bulk resistance exceeds 1 MΩ with impurities

Bulk conductivity is unaffected by magnetic fields

High electron mobilities achieved in related structures

Abstract

The two-dimensional topological insulator state in InAs/GaSb quantum wells manifests itself by topologically protected helical edge channel transport relying on an insulating bulk. This work investigates a way of suppressing bulk conductivity by using gallium source materials of different degrees of impurity concentrations. While highest-purity gallium is accompanied by clear conduction through the sample bulk, intentional impurity incorporation lead to a bulk resistance over 1 M\Omega. This resistance was found to be independent of applied magnetic fields. Ultra high electron mobilities for GaAs/AlGaAs structures fabricated in a molecular beam epitaxy system used for the growth of Sb-based samples are reported.