  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.
