Quantum beats of homogeneously broadened excitons in GaN

The polarization dependence of quantum beats from homogeneously broadened excitons in a high quality GaN epitaxial layer is studied. The wurtzite GaN epitaxial layers are grown to a thickness of 100 μm by vapor phase epitaxy into a sapphire substrate. The second harmonic of a Kerr lens mode-locked Ti-sapphire laser is used. In the collinear polarization configuration, the beats start with a maximum at τ = 0. In the crossed linear polarization, the beats start with a minimum and exhibit a π-phase shift compared to the collinear case. The decay time is 0.67 ps in the collinear polarization configuration and 0.60 ps in the crossed linear polarization configuration.