Monte Carlo Simulations of Intersubband Hole Relaxation in a GaAs/AlAs Quantum Well

An ensemble Monte Carlo code has been developed for the simulation of hole relaxation processes in a GaAs/AlAs quantum well. The code includes a realistic k.p model of the valence subbands and corresponding wavefunctions. Intra- and inter-subband phonon scattering rates are calculated for polar and non-polar interactions via both optical and acoustic modes. The code is used to simulate the cooling of non-equilibrium photogenerated hole populations. A lifetime of 90 fs is extracted for optical phonon mediated depopulation of the 4th subband at 77K. By contrast, the 2nd subband exhibits fast re-population, but slow de-population, with extracted lifetimes of up to 160 ps. The slow depopulation is attributed to the small energy separation of the 1st and 2nd subbands (less than the optical phonon energy) and the large density of states in the 2nd subband off-zone-centre minimum.