Ultrafast decay of photoluminescence from high-density excitons inAlxGa1−xNmixed crystals: Diffusive propagation of exciton-polaritons

Abstract

We report on the ultrafast decay dynamics of photoluminescence (PL) in highly excited ${\text{Al}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{N}$ mixed crystals under exciton resonant excitation at low temperatures. When the excitation intensity is increased, the P-band emission appears due to exciton-exciton inelastic scattering processes. The PL intensity of the P band decays rapidly, with a much shorter decay time than the radiative recombination time of the excitons. We show that the ultrafast PL decay dynamics can be understood as due to the disorder-induced diffusive propagation of photonlike exciton-polaritons in ${\text{Al}}_{x}{\text{Ga}}_{1\ensuremath{-}x}\text{N}$ mixed crystals.