Photoluminescence dynamics of excitons at the mini-Brillouin-zone edge in a GaAs/AlAs superlattice

摘要

We have investigated the photoluminescence (PL) dynamics of excitons at the mini-Brillouin-zone edge (k_z=π/D), the so-called π point, in a GaAs/AlAs superlattice (SL): D is a SL period. Under the resonant excitation condition of the first quantized (n=1) heavy-hole (HH) exciton at the r point (k_z=0), it was found that the PL band of the n=1HH exciton at the n point is observed from time-resolved PL spectra. The temporal profile of the PL of the π-point exciton exhibits a considerable delay time, ~40 ps, to that of the T-point exciton and a very short decay time, ~12 ps. Note that the PL of the π-point exciton has been never observed under off-resonant excitation of the T-point exciton. The delay time is attributed to the transit time from the T point to the π point in the mini-Brillouin zone. The very short decay time results from that the π point is a metastable state in the miniband dispersion. The mechanism of the transit process of the excitons is discussed from aspects of excitation-power dependence and scattering by folded longitudinal acoustic phonons peculiar to the SL.