The electronic states in quaternary GaInAsSb/AlGaAsSb strained quantum well (QW) structures grown by molecular beam epitaxy have been investigated both theoretically and experimentally. For Ga 0.75 In 0.25 As 0.04 Sb 0.96 /Al 0.22 Ga 0.78 As 0.02 Sb 0.98 strained multiple quantum wells (MQWs), strong luminescence, and well-resolved excitonic absorption peaks are observed even at room temperature, which is indicative of the good quality of our quaternary sample. By fitting the experimental results to the theoretical calculations, we find that the light holes are in Ga 0.75 In 0.25 As 0.04 Sb 0.96 well regions (type I MQWs) and the conduction band offset ratio Q c = 0.66 ± 0.01. The critical temperature for the excitonic-polaritonmechanical-exciton transition in this quaternary MQW structure was found to be ∼40 K. The measured intersubband absorption of about 10.7 µm is in good agreement with the theoretical calculation. The transition from type I MQWs to type II MQWs for light holes is also predicted theoretically. In the photoluminescence spectra the sharp exciton resonances have been attributed to localized excitons for temperature 80-100 K and to free excitons at higher temperatures up to room temperature. We conclude that the dominant luminescence quenching mechanism in this quaternary system is mainly that of the trapped excitons thermalizing from the localized regions below 100 K, and the thermal carrier activation from the first electron and heavy-hole subbands to the second electron and heavy-hole subbands at higher temperatures. The strength of the excitonphonon coupling is determined from the linewidth analysis. The inhomogeneous linewidth and homogeneous broadening in both MQW and single-quantum-well (SQW) structures have been discussed. We conclude that the experimental result of stronger exciton-phonon coupling in the quaternary SQW structure will lead to partial ionization of excitons at higher temperatures (above 125 K), in good agreement with the line-shape analysis of the luminescence spectra which clearly shows the presence of band-to-band recombination.

Extended balance equations accounting for the conduction-valence interband impact ionization (II) process in semiconductor heterostructures are presented. The II effect and terahertz (THz) field influence on electron transport in InAs/AlSb heterostructures is studied. It is shown that the II process usually results in a decrease in electron velocity and temperature when compared to the case without the II process. Qualitative agreement is obtained between the calculated electron-hole generation rates and available experimental data. Comparison with published experimental data on THz-driven heterostructures is also made.