Optical gain in GaInN/GaN heterostructures

By optical gain spectroscopy we have studied the fundamental laser properties of GaInN/GaN heterostructures grown on sapphire. Utilizing the stripe excitation method we have measured optical gain spectra at room temperature. Due to the low symmetry of the wurtzite structure and the resulting splitting of the uppermost valence bands, we find optical gain only for the TE mode. Our analysis shows that the optical gain is due to direct band-to-band transitions in an electron-hole plasma. For gain amplitudes typically found in lasers, we find carrier densities up to 3 x 10(19) cm(-3), which are likely to lead to rather large threshold current densities. (C) 1996 American Institute of Physics.