Extremely slow energy relaxation of a two-dimensional exciton in a GaAs superlattice structure

Abstract

Time-resolved photoluminescence spectra of a two-dimensional exciton in a GaAs superlattice structure were measured as a function of photon energy from a picosecond dye laser. When the photon energy of the excitation laser is close to the luminescence of the heavy-hole exciton, the rise time of the photoluminescence is very short. However, in a sample of high quality, an extremely slow rise time of 400 ps was observed during subband excitation. Three different relaxation processes, such as the relaxation of the heavy-hole exciton band, the relaxation from the electron-hole pair to the heavy-hole exciton, and the relaxation from the light-hole exciton to the heavy-hole exciton, are proposed. The relaxation time determined in the heavy-hole exciton band is (45\ifmmode\pm\else\textpm\fi{}20 ps)/meV, the generation rate of the heavy-hole exciton from the bottom of the electron-hole pair is 1/(190\ifmmode\pm\else\textpm\fi{}20 ps), and the generation rate of the heavy-hole exciton from the light-hole exciton is 90\ifmmode\pm\else\textpm\fi{}20 ps.