Quantum beats of free and bound excitons in GaN

We present spectrally resolved and time-integrated four-wave mixing measure ments at coherent dynamics of bound excitons in a high-quality GaN epilayer . Coherent excitation, with co-circular polarized light, of the neutral don or-bound excitons (D X-0) and A excitons (X-A) results in quantum beats, co rresponding to the energy splitting between D X-0 and X-A. The temperature- dependent dephasing rate is used to deduce the strength of the D X-0-acoust ic-phonon interaction via the homogeneous linewidth. (C) 2001 American Inst itute of Physics.