We report an extensive study of the excitonic properties of freestanding and heteroepitaxial GaN samples using continuous-wave reflectivity and time-resolved autocorrelation measurements. The coherent impulse response of free excitons is recorded by using an interferometric correlation technique. Excitonic parameters of GaN are deduced from the combined analysis of both experiments. Oscillator strengths and transition energies are studied as a function of the residual biaxial strain of the sample and temperature-dependent measurements are used to determine the parameters of the exciton-phonon interaction in GaN.

• Received 21 December 2006

DOI:https://doi.org/10.1103/PhysRevB.77.045206