Comparison of exciton-biexciton with bound exciton-biexciton dynamics in GaN: Quantum beats and temperature dependence of the acoustic-phonon interaction

The polarization dependence of biexcitonic signals and quantum beats between A-excitons (X_A) and A-biexcitons (X_AX_A) in a high-quality GaN epilayer is measured by spectrally-resolved and time-integrated four-wave mixing. With cross-linear polarised light, mixed beats with two periods are observed: the first beating period corresponds to the energy splitting between X_A and X_AX_A, and agrees well with the calculated X_AX_A binding energy; while the second beating period corresponds to that between X_A and donor bound excitons (D⁰X). The temperature-dependent homogeneous linewidth shows that the D⁰X has a larger acoustic phonon coupling coefficient than the X_AX_A. We also measured the polarization dependent B-biexciton (X_BX_B) signal. The effective masses for the A- and B-hole were deduced from the binding energy.