Systematic investigation on topological properties of layered GaS and GaSe under strain

Abstract

The topological properties of layered β-GaS and ε-GaSe under strain are systematically investigated by ab initio calculations with the electronic exchange-correlation interactions treated beyond the generalized gradient approximation (GGA). Based on the GW method and the Tran-Blaha modified Becke-Johnson potential approach, we find that while ε-GaSe can be strain-engineered to become a topological insulator, β-GaS remains a trivial one even under strong strain, which is different from the prediction based on GGA. The reliability of the fixed volume assumption rooted in nearly all the previous calculations is discussed. By comparing to strain calculations with optimized inter-layer distance, we find that the fixed volume assumption is qualitatively valid for β-GaS and ε-GaSe, but there are quantitative differences between the results from the fixed volume treatment and those from more realistic treatments. This work indicates that it is risky to use theoretical approaches like GGA that suffer from the band gap problem to address physical properties, including, in particular, the topological nature of band structures, for which the band gap plays a crucial role. In the latter case, careful calibration against more reliable methods like the GW approach is strongly recommended.

Crystal structure and energy bands of (Ga/In)Se and Cu(In,Ga)Se2 semiconductors in comparison

“…Out of many earlier calculations, we single out that of An et al. () done on ‐GaSe (also studied by us but omitted in the present report for brevity), using notably WIEN2k, PBEsol, and mBJ, in a row of other XC flavours. An important message from this work concerning our present one is that the spin‐orbit interaction (neglected in our case), apparently, has no noticeable effect onto the lattice parameters and the band gap values of GaSe.…”

Temperature-Dependent Photoluminescence Emission from Unstrained and Strained GaSe Nanosheets

“…It demonstrates interesting electrical and optical properties, such as a high on/off ratio [ 7 , 14 ], large anisotropic Hall mobility [ 7 , 15 ], good gas sensibility [ 16 ], and strong second-harmonic generation [ 17 ]. More recently, it has also been shown that the electronic band structures and PL intensity of layered GaSe can be effectively tuned via the elastic strain engineering [ 18 , 19 , 20 ]. These flexible electrical and optical properties make it an appealing candidate for mechanically compliant optoelectronics with applications in piezo-phototronics, optoelectronics, wearable devices and human–machine interfaces [ 21 , 22 , 23 , 24 ].…”

Mexican Hat and Rashba Bands in Few-Layer van der Waals Materials

“…Results calculated from PBE and HSE functionals are given, and results with and without spin-orbit coupling are listed. The effects of AA' versus AA stacking order of GaS and AA' versus ǫ stacking order of GaSe 72,73 are also compared.…”