Dynamics of excitons bound to nitrogen isoelectronic centers in GaAs

A detailed analysis of the dynamics of excitons bound to two nitrogen atoms forming an isoelectronic center of C-2v symmetry in GaAs is presented. The temperature dependence of photoluminescence (PL) intensities under both continuous and pulsed excitations reveals (1) overall decay rates significantly slower than that of spontaneous emission, (2) a decay rate anisotropy between states of orthogonal symmetry representations, and (3) a complementary behavior of relative intensities measured from states of identical symmetry representations. A comprehensive model of the exciton fine structure and the exciton dynamics allows the determination of the strength of the exchange and crystal-field interactions, the light- and heavy-hole splitting and composition of exciton states, the exciton capture time, the rates of spontaneous and nonradiative emission, and the rates of interlevel transfers induced by interactions with nuclear spins and by longitudinal acoustic phonons. It is found that the rate of electron spin flips is comparable to that measured in quantum dots but that the near degeneracy of light and heavy holes results in an efficient transfer channel between light-and heavy-hole states of identical symmetry representation.