Theoretical and experimental studies of electronic band structure for GaSb_(1-x)Bi_x in the dilute Bi regime

摘要

Photoreflectance (PR) spectroscopy was applied to study the band gap in GaSb_(1-x)Bi_x alloys with Bi < 5%. Obtained results have been interpreted in the context of ab initio electronic band structure calculations in which the supercell (SC) based calculations are joined with the alchemical mixing (AM) approximation applied to a single atom in the cell. This approach, which we call SC-AM, allows on the one hand to study alloys with a very small Bi content, and on the other hand to avoid limitations characteristic of a pure AM approximation. It has been shown that the pure AM does not reproduce the GaSb_(1-x)Bi_x band gap determined from PR while the agreement between experimental data and the ab initio calculations of the band gap obtained within the SC-AM approach is excellent. These calculations show that the incorporation of Bi atoms into the GaSb host modifies both the conduction and the valence band. The shift rates found in this work are respectively -26.0 meV per % Bi for the conduction band and 9.6 meV per % Bi for the valence band that consequently leads to a reduction in the band gap by 35.6 meV per % Bi. The shifts found for the conduction and valence band give a ～27% (73%) valence (conduction) band offset between GaSb_(1-x)Bi_x and GaSb. The rate of the Bi-related shift for the split-off band is -7.0 meV per % Bi and the respective increase in the spin-orbit split-off is 16.6 meV per % Bi.