Temperature dependent photon echoes of a GaN thin film

UV photon echoes from a ∼120 nm GaN thin film exhibit a biexponential decay attributed to the coherence loss of slowly and rapidly decaying excitons corresponding to excitons with different degrees of localization or trapping in this material. Both exciton populations are strongly inhomogeneously broadened. For one exciton type, T2 is ∼300 fs at 10 K and ≤25 fs at 300 K; for the other, T2 is pulse-width limited (≤25 fs) at all temperatures. At low temperatures, coherence decay predominantly results from impurity and defect site interactions. At higher temperatures, strong exciton-LO phonon coupling dominates dephasing.