INAS GA1-XINXSB AND INAS/AL1-XGAXSB SUPERLATTICES FOR INFRARED APPLICATIONS/

We report a full-scale pseudopotential study of the optical properties of InAs/Ga(1-x)ln(x)Sb and InAs/Al1-xGaxSb superlattices, with partic ular emphasis on the infrared range of wavelengths. For both structure s we examine the detailed origin of the absorption response and how cu toff wavelength varies with the period of the superlattice and with th e alloy concentration. This entails a discussion of how wavefunction l ocalization, band mixing and energy band dispersion can affect the abs orption coefficient. Particular attention is paid to structures with c utoff wavelength in the ranges 2-5 mu m and 10-13 mu m. Calculated abs orption spectra are compared with examples obtained experimentally. Al though agreement between the spectra is good, it is found that neither the sharp features nor the absolute magnitude is reproduced adequatel y by the electronic structure obtained from idealized systems. Compari son of the bandgap with the gap between the highest two valence states allows structures where certain Auger recombination processes may be inhibited to be indicated. The effects of alloy scattering in the InAs /Ga(1-x)ln(x)Sb system has also been investigated. A second-order pert urbation theory calculation of the linewidth associated with the alloy potential suggests that the effects of alloy scattering are too large to be modelled as a perturbation of the virtual crystal case. A full- scale treatment is required to quantity this effect.