Kinetics of free-exciton luminescence in GaAs

Exciton-polariton photoluminescence kinetics under short-pulse excitation in nominally undoped GaAs has been investigated. A delayed onset revealing the energy relaxation of electrons and polaritons has been observed. In an ultrapure sample (${\mathit{N}}_{\mathit{D}}$∼${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}3}$) the maximum luminescence is reached after a considerable delay of 4 ns. Energy relaxation speeds up with an increase in impurity concentration and depends on the type of conductivity. At a high repetition rate, the next excitation pulse causes fast quenching of polariton luminescence in the vicinity of exciton resonance because of heating of excitons by photoexcited hot electrons.