  A systematic theoretical study of the electronic and optical properties of
Ga$_{1-x}$In$_x$As self-assembled quantum-wires (QWR's) made of short-period
superlattices (SPS) with strain-induced lateral ordering is presented. The
theory is based on the effective bond-orbital model (EBOM) combined with a
valence-force field (VFF) model. Valence-band anisotropy, band mixing, and
effects due to local strain distribution at the atomistic level are all taken
into account. Several structure models with varying degrees of alloy mixing for
lateral modulation are considered. A valence force field model is used to find
the equilibrium atomic positions in the QWR structure by minimizing the lattice
energy. The strain tensor at each atomic (In or Ga) site is then obtained and
included in the calculation of electronic states and optical properties. It is
found that different local arrangement of atoms leads to very different strain
distribution, which in turn alters the optical properties. In particular, we
found that in model structures with thick capping layer the electron and hole
are confined in the Ga-rich region and the optical anisotropy can be reversed
due to the variation of lateral alloying mixing, while for model structures
with thin capping layer the electron and hole are confined in the In-rich
region, and the optical anisotropy is much less sensitive to the lateral alloy
mixing.
