Direct calculation of the transport properties of disordered AlAs/GaAs superlattices from the electronic and phonon spectra

We have calculated from first principles the recently measured electron and hole transport of disordered AlAs/GaAs superlattices, in which the individual layer thicknesses n,m,n^',m^',... of sequence (AlAs)ₙ(GaAs)ₘ(AlAs)ₙ^'(GaAs)ₘ^'... are 1, 2, or 3, selected at random with equal probabilities. First, the near-edge electronic states are calculated using a three-dimensional pseudopotential representation for a {~}2000-ML cell. The results are then modeled by an effective-mass approximation, thus obtaining the electronic states in a wider energy range. All electronic states are found to be localized in the superlattice direction. Second, the phonon-assisted-hopping probabilities between different localized electronic states are calculated from first principles, including contributions of polar optical, acoustic deformation-potential, and acoustic piezoelectrical effects. Third, the master equation describing electron transport via phonon-assisted hopping is addressed using Monte Carlo simulations. The resulting transport properties versus temperature are analyzed according to dispersive transport theories, including the crossover from dispersive to equilibrium transport. A simple model for the photoluminescence process is proposed on the basis of the transport calculations. Our results agree qualitatively with recent experimental data.