InAs/ and InAs/ superlattices for infrared applications

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Abstract
We report a full-scale pseudopotential study of the optical properties of InAs/ and InAs/ superlattices, with particular emphasis on the infrared range of wavelengths. For both structures we examine the detailed origin of the absorption response and how cutoff wavelength varies with the period of the superlattice and with the alloy concentration. This entails a discussion of how wavefunction localization, band mixing and energy band dispersion can affect the absorption coefficient. Particular attention is paid to structures with cutoff wavelength in the ranges 2-5 m and 10-13 m. Calculated absorption spectra are compared with examples obtained experimentally. Although agreement between the spectra is good, it is found that neither the sharp features nor the absolute magnitude is reproduced adequately by the electronic structure obtained from idealized systems. Comparison 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/ system has also been investigated. A second-order perturbation 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 quantify this effect.