Excitation-dependent carrier dynamics in Al-rich AlGaN layers and multiple quantum wells
Résumé
.The combined temporally, spatially and spectrally‐resolved optical techniques, namely the photoluminescence, light induced transient grating, and differential reflectivity were used for investigation of excitation‐dependent PL efficiency, exciton lifetime, and diffusion coefficient in Si‐doped Al‐rich multiple quantum wells and epilayers at various temperatures. Novel features of carrier recombination and in‐plane diffusion were observed. Low‐excitation radiative lifetime of 1–2 ns was found temperature‐independent in 80–150 K interval, while it sublinearly decreased with excitation at excess carrier densities above 1018 cm−3. The lifetime decrease correlated with the increase of diffusion coefficient, indicating excitation‐enhanced delocalization of localized excitons and therefore enhanced capture to nonradiative centers. The droop of photoluminescence efficiency with excitation was the strongest at 80–150 K due to strong delocalisation at low‐temperatures, while at higher temperatures the thermal activation prevailed in photoluminescence excitation dependence. The photoluminescence efficiency quenching at T > 200 K provided rather high activation energies of ∼100 and 160 meV for Al‐rich multiple quantum wells and epilayers, correspondingly.