Photoluminescence and optical gain in highly excited GaN

A systematic study of the near-band-edge photoluminescence of epitaxially grown GaN as a function of excitation density has been carried out. While at low densities free and bound-exciton emission lines govern the spectrum, new luminescence bands are detected at densities above 1 MW/cm(2). Gain measurements and temperature-dependent investigations indicate that nonlinear processes like biexciton annihilation, exciton-exciton-scattering and stimulated A-LO-emission are dominant at low temperatures, while exciton-free-carrier scattering occurs at temperatures above 200 K.