Hot-electron cooling dynamics in photoexcited bulk and quantum-well Ga
As Structures were determined using time-correlated single-photon coun
ting of photoluminescence (PL) decay. Hot-electron cooling curves were
generated from analyses of the time-resolved PL spectra. The time con
stant characterizing the hot-electron energy-loss rate, tau(avg), was
then determined, taking into account electron degeneracy and the time
dependence of the quasi-Fermi-level. This analysis was also applied to
earlier data obtained by Pelouch et al. with the same samples, but ba
sed on PL up-conversion experiments with < 80 fs temporal resolution.
Both sets of experiments and analyses show that the hot-electron cooli
ng rate can be much slower in GaAs quantum wells compared (at the same
photogenerated carrier density) to bulk GaAs when this density is abo
ve a critical value. This critical density was found to range from hig
h 10(17) to low 10(18) cm-3, depending upon the experimental technique
; at the highest carrier densities, values of tau(avg) for quantum wel
ls were found to be many hundreds of ps.