Optical gain in the nitrides: are there differences to other III–V semiconductors?

We have studied the optical gain spectra in GalnN/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 GalnN/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.