Femtosecond three-pulse photon echo and transient grating studies of the yellow band of GaN

Using femtosecond three-pulse two-colour photon echo measurements we study the optical nonlinearity induced by pump and probe in the short time scale (< 500 fs) where the free induction decay and photon echo are the main contribution to observed signal and in a long time scale (up to 20 ps) in the trace of the population grating. The variation of the pump and probe wavelength and use of spectrally resolved measurements allows us to study the origin of the yellow band and the phase and energy relaxation properties of this band. The results suggest that the light emission in the yellow band is the recombination between shallow donors and deep acceptors and the carriers trapping time is very short.