First-Principles Calculations of Electronic Structures of New III--V Semiconductors: B_xGa_1-xAs and Tl_xGa_1-xAs alloys

We investigate the electronic structures of new semiconductor alloys B_xGa_1-xAs and Tl_xGa_1-xAs, employing first-principles calculations within the density-functional theory and the generalized gradient approximation. The calculation results indicate that alloying a small Tl content with GaAs will produce larger modifications of the band structures compared to B. A careful investigation of the internal lattice structure relaxation shows that significant bond-length relaxations takes place in both the alloys, and it turns out that difference between the band-gap bowing behaviours for B and Tl stems from the different impact of atomic relaxation on the electronic structure. The relaxed structure yields electronic-structure results, which are in good agreement with the experimental data. Finally, a comparison of formation enthalpies
indicates that the production Tl_xGa_1-xAs with Tl concentration of at least 8% is possible.