Quantum beats of homogeneously broadened excitons in GaN

It has been observed that the phase of quantum beats shifts by /spl pi/ if the incident polarization is changed from collinear to crossed linear. Schmitt-Rink et al. (1992) explained this using a single particle model based on the band structure. However, in their experimental results they also observed a decay rate and intensity dependence on the incident polarization, which their model cannot explain. On the other hand, Saiki et al. (1994) proposed an excitonic model and found that the decay rate and intensity changes depending on if the system is homogeneously or inhomogeneously broadened when changing the incident polarization. In this paper, we present the polarization dependence of quantum beats from homogeneously broadened excitons in a high-quality GaN epitaxial layer. The observed /spl pi/-phase shift of quantum beats can be explained with the model for GaAs quantum wells proposed by Schmitt-Rink et al. However, it can neither explain the signal intensity dependence nor the differences between the two cases of homogeneously and inhomogeneously broadened transitions. We analyze our data on the basis of the model by Saiki et al. for the case of homogeneously broadened transitions and achieve a good qualitative agreement. Not only is the polarization dependence of the decay rate accurately modeled but also the intensity as a function of laser pulse polarization.