Theory of optical anisotropy in quantum-well-wire arrays with two-dimensional quantum confinement

The effective bond-orbital model is used to calculate the conduction- and valence-subband structures of recently grown epitaxially buried GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/AlAs quantum-well-wire arrays. The model incorporates the coupling of the degenerate spin-3/2 valence bands and the s-like conduction bands. Band-structure parameters of all the materials involved are taken into account as well as the lateral intermixing of species, which has been observed in such structures. The quantum-wire (QWR) array is an intermediate case between quasi-one- and quasi-two-dimensional structures; the dispersion perpendicular to the QWR’s is explainable in the combined terms of lateral confinement and zone folding. We calculate optical matrix elements within the model for light polarized parallel and perpendicular to the QWR’s. When lateral intermixing is taken into account, the carriers occupy preferentially the nonmodulated part of the structure and exhibit only very weak optical anisotropy. Thus, the structure behaves like a two-dimensional rather than a one-dimensional system. We discuss our results in the context of the observed photoluminescence excitation spectra. It is found that band mixing, lateral diffusion, and the interplay of quasi-one- and quasi-two-dimensional properties play important roles in determining the electronic and optical properties.