Dynamics of resonantly excited excitons in GaN

We present resonant fs pump-probe reflectance measurements of excitons in w urtzite GaN epilayers at different lattice temperatures. At 4 K we find tha t the exciton dynamics is dominated by trapping at defects via acoustic-pho non emission on a time scale of 16 ps. At temperatures above 60 K we observ e a much longer relaxation component of 375 ps, which is due to radiative r ecombination of free excitons. The results are in good agreement with theor etical predictions. [S0163-1829(98)50748-5].