Temperature and excitation intensity dependent luminescence lifetime studies on GaAs/AlGaAs quantum well structure

Abstract

Time-resolved photoluminescence spectra of a GaAs/AlGaAs quantum well structure with uncoupled four single quantum wells having 2 nm, 4 nm, 6 nm, and 10 nm well widths, respectively, reveal that exciton and free carrier recombination processes in the quantum wells are dependent on excitation intensity. At a low excitation level, exciton lifetimes were measured as 100 ps, 110 ps, 150 ps, and 220 ps for 2 nm, 4 nm, 6 nm, and 10 nm wells, respectively, at 10 K, which confirms quantum confinement effect. Exciton lifetimes increase linearly with an increase in temperature in larger wells(6 nm and 10 nm) but do not show linearity in 2 nm and 4 nm wells, which shows that excitons in smaller wells are likely to be localized on interface defects.1 This result is in accordance with photoluminescence spectrum and rise-time measurement. As excitation intensity increases, free carrier recombination becomes dominant by exciton screening effect and the time evolution of luminescence has different features from those at low excitation levels. We will disscus how excitons collapse into free carriers by exciton screening and how free carriers in each quantum well recombine, from the picosecond luminescence lifetime measurement at various temperatures (10–100 K) and excitation intensities.