Degenerate four-wave-mixing spectroscopy on epitaxially laterally overgrown GaN: Signals from below the fundamental absorption edge

We performed photoluminescence (PL) and degenerate four-wave-mixing (FWM) s pectroscopy in epitaxially laterally overgrown GaN at 10 K. Optical transit ions based on exciton complexes such as biexciton emission, exciton-exciton scattering, electron-hole plasma, and so on, were revealed by PL under a w ide range of excitation densities. The FWM signals were observed from state s below the fundamental excitonic absorption edge, showing that nonlinear p hotoswitching can be performed with a transmittance geometry. The origin of such nonlinearlity was discussed by correlating with feasible many-body ef fects between excitons, biexcitons, and free carriers. (C) 2001 American In stitute of Physics.