Effects of alloying and hydrostatic pressure on electronic and optical properties of GaAs-Al_{x}Ga_{1-x}As superlattices and multiple-quantum-well structures

We have used our pseudopotential scheme to calculate electronic and optical properties of GaAs-${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As superlattices and multiple-quantum-well structures as a function of alloying (0≤x≤1), hydrostatic pressure (0–50 kbar), and band offsets. We have obtained a full description of the electronic states both near the band edges and well into the range of energies above the confining barriers. In particular, we have shown how alloying can be used to mix Γ-like states with X-like states. Such mixing can lead to dramatic changes in the rapidly varying parts of the superlattice wave functions and alter appreciably the observable optical properties associated with such states. We also show that similar effects can be produced by the application of hydrostatic pressure. The electronic structure and optical properties of periodic structures with GaAs layers of width up to 102 Å and ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As layers of width up to 514 Å have been studied. We show how mixing in wave-vector space between confined states and between confined states and extended bulk Bloch states leads to changes in observable properties, some of which can be exploited in order to determine band offsets. A representative set of data on the pressure dependence of optical spectra is used to make a comparison between theoretical and experimental results.