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

Abstract

First principles simulations are conducted to shed light on the question of whether a twodimensional 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.

Structure prediction of epitaxial inorganic interfaces by lattice and surface matching with Ogre

“…These U values have produced band structures in good agreement with angle-resolved photoemission spectroscopy (ARPES) for InAs and InSb surfaces. 19 The Tkatchenko-Scheffler (TS) 91 pairwise dispersion method was used to account for the van der Waals interactions at the interface. A plane-wave cutoff of 450 eV was adopted.…”

“…Different interface configurations may produce different properties. 15,[17][18][19] Moreover, defects and disorder may be detrimental to the functionality of a device. In particular, quantum devices may be extremely sensitive.…”

“…Owing to quantum size effects, a large number of layers of each material must be included in the interface model to converge its properties. 19,57,58 Moreover, domain matched interfaces may require large supercells. This often amounts to models containing hundreds of atoms.…”

Dependence of the electronic structure of the EuS/InAs interface on the bonding configuration

“…The U ef f values obtained therein were U In,p ef f = -0.5 eV, U As,p ef f = -7.5 eV, and U Eu,f ef f = 8.4 eV. The PBE+U(BO) method with these parameters has been used successfully for InAs surfaces [54] and the InAs/GaSb interface [55]. A plane-wave basis set was used with a kinetic energy cutoff of 450 eV.…”

“…Recently, we have developed a method of machine learning the optimal value of the effective Hubbard U parameter by Bayesian optimization (BO) [46]. The PBE+U(BO) method has been demonstrated to provide a reliable description of bulk EuS and InAs [46], as well as InAs surfaces [54] and interfaces [55]. Here, we use PBE+U(BO) to study the electronic structure of the EuS/InAs (001) interface.…”