First-principles calculations of bismuth induced changes in the band structure of dilute Ga-V-Bi and In-V-Bi alloys: chemical trends versus experimental data
Bi-induced changes in the band structure of Ga–V–Bi and In–V–Bi alloys are calculated within the density functional theory (DFT) for alloys with Bi ≤3.7% and the observed chemical trends are discussed in the context of the virtual crystal approximation (VCA) and the valence band anticrossing (VBAC) model. It is clearly shown that the incorporation of Bi atoms into III–V host modifies both the conduction band (CB) and the valence band (VB). The obtained shifts of bands in GaP1−xBix, GaAs1−xBix, GaSb1−xBix, InP1−xBix, InAs1−xBix, and InSb1−xBix are respectively, 15, −29, −16, −27, −15, and −10 meV/%Bi for CB, 82, 62, 16, 79, 45, and 16 meV/%Bi for VB, and −17, −3, −2, −8, −6, and 14 meV/%Bi for spin–orbit split off band. The Bi-induced reduction of the band gap is very consistent with the available experimental data. The chemical trends observed in our calculations as well as in experimental data are very clear: in a sequence of alloys from III–P–Bi to III–Sb–Bi the Bi-induced changes in the band structure weaken. For dilute GaSb1−xBix and InSb1−xBix alloys the band structure modification, in the first approximation, can be described within the VCA, while for Ga–V–Bi and In–V–Bi alloys with V = As or P another phenomenological approach is needed to predict the Bi-induced changes in their band structure. We have found that a combination of the VCA with the VBAC model, which is widely applied for highly mismatched alloys, is suitable for this purpose. The chemical trends for III–V–Bi alloys observed in our DFT calculations are also exhibited by the coupling parameter which describes the magnitude of interaction between Bi-induced levels and VB states in the VBAC model. This coupling parameter monotonously decreases along the sequence of alloys from III–P–Bi to III–Sb–Bi.