OPTIMIZED TIGHT-BINDING VALENCE BANDS AND HETEROJUNCTION OFFSETS IN STRAINED III-V SEMICONDUCTORS

An optimized nearest-neighbor tight-binding description of valence bands in strained-layer III-V semiconductors is developed and applied to the calculation of valence-band offsets at strained heterojunctions. It is first shown that a single set of universal interatomic matrix elements can be found which, when appropriately scaled for bond length, simultaneously provide near-optimum tight-binding predictions of valence-band uniaxial deformation potentials, trends in photoelectric thresholds, and valence bandwidths for the common III-V compounds. Application of the optimized tight-binding model to the calculation of valence-band offsets at strained heterojunctions is then discussed, and one simple approach is described which combines a fully strain-dependent version of the optimized tight-binding model with Tersoff's quantum-dipole heterojunction model. Offsets calculated using this combined approach are shown to agree with experimental data better than either strain-dependent natural tight-binding offsets or offsets calculated directly from Tersoff's model. Finally, convenient quadratic expressions for the composition dependence of light- and heavy-hole valence-band offsets, as calculated using the combined approach, are tabulated for several strained and unstrained ternary-on-binary III-V heterojunctions. The balance between accuracy and simplicity offered by our approach should render it useful for exploratory heterojunction device modeling.