Comparative study of band-structure calculations for type-II InAs/InxGa1-xSb strained-layer superlattices.

Abstract

Short-period InAs/${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$Sb superlattices may allow strong optical transitions in the long-wavelength infrared (g10 \ensuremath{\mu}m) spectral region. Absorption calculations can be difficult, however, because of the strongly type-II interface and because of the large lattice mismatch. We present a comparative study of band-structure calculations for strained-layer type-II InAs/${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$Sb superlattices grown on GaSb. The energy of superlattice band gaps (${\mathit{E}}_{\mathit{g}\mathit{s}}$) and the cutoff wavelengths (${\ensuremath{\lambda}}_{\mathit{c}}$) are computed in the empirical tight-binding, effective-bond-orbital, and 8\ifmmode\times\else\texttimes\fi{}8 k\ensuremath{\cdot}p models. In the empirical tight-binding model (ETBM) the strain is included by scaling the matrix elements according to Harrison's universal 1/${\mathit{d}}^{2}$ rule and by appropriately modifying the angular dependence. The bond-orbital model (EBOM) and k\ensuremath{\cdot}p calculations include the strain via the deformation-potential theory. We find in all cases that the superlattice band gap decreases rapidly with increasing x and that the proper inclusion of strain is critical in the ETBM. Our results compare favorably with existing experiments. In addition, we compare directly the results of the EBOM and k\ensuremath{\cdot}p models. Contrary to expectations, the two models give quite different results for InAs/InSb superlattices.