Monte Carlo simulation of intersubband relaxation in single and multiple quantum wells

We studied intersubband relaxation of carries during ultrafast photoexcitation in single and coupled quantum wells using ensemble Monte Carlo simulation, Intra- and intersubband scattering due to polar and nonpolar optical phonons, acoustic phonons, and intercarrier scattering are included in the simulation. The polar optical mode description is given in terms of a two-pole dielectric continuum model for the alloy barriers. In the present work we focus on relaxation when the 2-1 subband spacing is smaller than the optical phonon energy so that suppression of the intersubband polar optical phonon scattering rate occurs. Our results for a single well show that intercarrier intersubband scattering dominates over acoustic phonon scattering during the initial relaxation of carriers from 2-1, with a strong contribution due to polar optical phonon emission from the tails of the heated distributions as well. We have studied optical pumping for a 3 level coupled quantum well system in which ΔE₁₂ is less than h approximately ega₀, and calculate the change in occupancy of the excited subbands through pumping of the 1-3 transition.