PHONON-SCATTERING AND MOBILITY OF HOLES IN A GAAS/ALAS QUANTUM-WELL

Rates for hole-phonon scattering in a GaAs/AlAs quantum well are calculated using an eight-band k . p method. The method includes the effects of heavy hole-light hole mixing on the scattering matrix elements, subband energy dispersions and densities of states. The scattering rates exhibit distinct structure; arising on the one hand, from the strong k parallel-to dependence of the matrix elements (due to band mixing), and on the other, from large peaks in the densities of states at subband energy minima which are displaced from the zone centre. The rates for intasubband scattering by both optical and acoustic phonons are larger than the principal intraband rates for holes in bulk GaAs. However, the rates for intersubband scattering are reduced by band mixing effects, and are all considerably smaller than the principal bulk interband rate. The scattering rates are used as a database for Monte Carlo simulations of steady state hole transport in the GaAs/AlAs quantum well. The low field 2D hole mobility at 77 K is estimated to be some 30% lower than the phonon-limited bulk mobility, and this is attributed to the stronger acoustic phonon scattering in the quantum well. At higher fields, strong intrasubband polar optical scattering is evident, giving rise to an anomolous repopulation of the highest valence subband.