Optical gain in the nitrides: Are there differences to other III-V semiconductors?

We have studied the optical gain spectra in GaInN/GaN and GaN/AlGaN double heterostructures and quantum wells at room temperature employing the stripe-excitation method. We compare the results with data for other III-V semiconductors. The optical gain is strongly anisotropic, with almost no gain for the TM mode. For quantum wells, the material gain increases with decreasing well width as expected. Whereas for GaInN/GaN structures only a single gain peak is observed, consistent with a free-carrier gain model, measurements on GaN/AlGaN structures reveal two peaks, which are assigned to localized exciton and exciton-LO-phonon gain. (C) 1997 Elsevier Science S.A.