First principles feasibility assessment of a topological insulator at the InAs/GaSb interface

TL;DR

This study uses first principles simulations to evaluate the potential for a two-dimensional topological insulator phase at the InAs/GaSb interface, comparing it with HgTe/CdTe and exploring external electric field effects.

Contribution

The paper provides the first detailed first-principles analysis of the InAs/GaSb interface's topological properties, highlighting conditions needed to achieve the topological insulator phase.

Findings

HgTe/CdTe achieves band crossing at 5.1 nm thickness

InAs/GaSb gap narrows but does not close up to 15 nm

External electric field can induce band crossing in InAs/GaSb

Abstract

First principles simulations are conducted to shed light on the question of whether a two-dimensional topological insulator (2DTI) phase may be obtained at the interface between InAs and GaSb. To this end, the InAs/GaSb interface is compared and contrasted with the HgTe/CdTe interface. Density functional theory (DFT) simulations of these interfaces are performed using a machine-learned Hubbard U correction [npj Comput. Mater. 6, 180 (2020)]. For the HgTe/CdTe interface our simulations show that band crossing is achieved and an inverted gap is obtained at a critical thickness of 5.1 nm of HgTe, in agreement with experiment and previous DFT calculations. In contrast, for InAs/GaSb the gap narrows with increasing thickness of InAs; however the gap does not close for interfaces with up to 50 layers (about 15 nm) of each material. When an external electric field is applied across the InAs/GaSb interface, the GaSb-derived valence band maximum is shifted up in energy with respect to the InAs-derived conduction band minimum until eventually the bands cross and an inverted gap opens. Our results show that it may be possible to reach the topological regime at the InAs/GaSb interface under the right conditions. However, it may be challenging to realize these conditions experimentally, which explains the difficulty of experimentally demonstrating an inverted gap in InAs/GaSb.