Optical properties of quaternary GaInAsSb/AlGaAsSb strained quantum wells

Abstract

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 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 well regions (type I MQWs) and the conduction band offset ratio . The critical temperature for the excitonic-polariton - mechanical-exciton transition in this quaternary MQW structure was found to be . The measured intersubband absorption of about 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 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 exciton - phonon 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.