Exciton diffusion in CdSe

In transient laser-induced grating experiments, the diffusion coefficients and lifetimes of free excitons are determined in CdSe at temperatures between 2 and 40 K and for different densities. We find that the diffusion coefficient D decreases and that the recombination lifetime ${\mathit{T}}_1$ increases with increasing temperature. The increase of ${\mathit{T}}_1$ with temperature is due to the release of excitons bound to impurities and to an increase of the radiative lifetime. From the measured D values for motion parallel and perpendicular to the crystal c axis, we extract momentum relaxation rates which are discussed in terms of exciton-acoustic-phonon scattering. In pure samples, and for lattice temperatures T