Structure and Electronic Properties of InSe and GaSe Polytypes

Equilibrium crystal structures, electron band dispersions, and bandgap values of layered GaSe and InSe semiconductors, each being represented by four polytypes, have been investigated within the density functional theory [1]. Several dispersion correction methods to the DFT, from empirical Grimme corrections to many-body dispersion schemes, have been assessed in comparison with experimental cell parameters [2]. Due to the high technical accuracy achieved, nearly degenerate energy-volume curves of different polytypes are resolved, and the conclusions concerning the relative stability of competing polytypes drawn [3]. The band structures are inspected using the modified Becke-Johnson (mBJ) scheme and hybrid HSE06 functional. Both methods nicely agree with the experimental results and with state-of-the-art GW calculations. Some discrepancies are identified in cases of close competition between the direct and indirect gap (e.g., in GaSe). The placement of bands are slightly differents for mBJ and HSE06.

[1] J. Srour, M. Badawi, F. El Haj Hassan, A. Postnikov, J. Chem. Phys. 149 (2018)
[2] J. Srour, M. Badawi, F.E.H. Hassan, A.V. Postnikov, Physica Status Solidi (B). 253 (2016) 1472
[3] J. Srour, A. Postnikov, M. Badawi, F.E.H. Hassan, Physica Status Solidi (B) 254 (2017) 1700120