Valence band splitting in bulk dilute bismides

Abstract

The electronic structure of bulk GaAs 1−x Bi x systems for different atomic configurations and Bi concentrations is calculated using density functional theory. The results show a Bi-induced splitting between the light-hole and heavy-hole bands at the Γ-point. We find a good agreement between our calculated splittings and experimental data. The magnitude of the splitting strongly depends on the local arrangement of the Bi atoms but not on the uni-directional lattice constant of the supercell. The additional influence of external strain due to epitaxial growth on GaAs substrates is studied by fixing the in-plane lattice constants.The following article has been submitted to Applied Physics Letters. If it is published, it will be found online at http://apl.aip.orgThe incorporation of relatively small concentrations of bismuth into semiconductor compounds is of growing interest because substitution of Bi not only allows for the engineering of the band gap E g 1 of III-V semiconductors but also of the spin-orbit splitting ∆ so 2 . It has been proposed that making ∆ so larger than E g should lead to a decrease of the nonradiative Auger losses which is important to improve the output characteristics of semiconductor lasers 3,4 .In addition to the intrinsic splitting between the spin-orbit split-off band (so) and the top-most valence bands, the degeneracy of the heavy-hole (hh) and light-hole (lh) bands at the Γ-point can also be lifted by symmetry reductions. A wellknown example is the valence band splitting (VBS) in III-V semiconductors caused by strain due to lattice-mismatched growth 5 . Experimentally, VBS was observed for GaAs 1−x Bi x layers grown lattice-mismatched on GaAs substrates 1,6,7 . To analyze the observations, Batool et al. 6 extracted the shear deformation potential for a Bi content up to x = 10.4 %. As previously shown for dilute nitrides 8 , the authors find that the shear deformation potential depends on the content of the substitute. However, in the case of GaAs 1−x N x the VBS shows a bowing which is absent for GaAs 1−x Bi x . In addition, a VBS of bulk GaAs 1−x Bi x has been observed in tight-binding calculations by Usman et al. 9 even though the authors do not further comment on it. They find an increase of the splitting in the case of compressive strain 10 which slightly underestimates the splitting reported by Batool et al. 6 .To systematically study Bi induced VBS, we use density functional theory (DFT) for the calculation of the band structures of dilute bismide semiconductors. Remarkably, our results show that a large VBS in the range of tens to more than hundred meV exists for bulk systems without any external strain. The magnitude of the splitting strongly depends on the local atomic arrangement of the Bi atoms in the GaAs lattice. Similar cluster-induced VBS has previously also been reported for GaAs 1−x N x 11 . For a given atomic configuration, a) Electronic mail: lars.bannow@physik.uni-marburg.de the VBS can be further increased when a lattice-mismatched growth is modeled by allowing ...

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