Monte Carlo Simulation of Sub-Picosecond Phenomena in Semiconductor Quantum Wells and Superlattices

We have modeled ultra-fast processes occurring during photoexcitation in AlGaAs/GaAs quantum wells using an ensemble Monte Carlo simulation. This simulation models the dynamics of quasi-two-dimensional electrons and holes confined within a single quantum well including the effects polar optical and transverse optical phonons, intervalley scattering, ionized impurities, and intercarrier scattering. The effect of nonequilibrium phonons and degeneracy are also included. We have used our simulation to compare to time resolved photoluminescence and transmission experiments in semiconductor quantum wells. For the latter experiments (W.H. Knox et al., Phys. Rev. Lett. 56, 1191 (1986)) performed at low excitation energies in the band, the results of our simulation show that electron-electron scattering is the dominant mechanism in accounting for the experimentally observed relaxation. While the electrons relax to form a thermalized distribution over 200 fs, the heavy holes generated at the same time relax within 50 fs, and the corresponding differential transmission spectrum is primarily determined by electron relaxation in the conduction band. Thermalization of the electrons with the cooler holes occurs over a longer time scale of 1 ps via inelastic intercarrier scattering.