Optical-Gain Measurements on GaN and Al_xGa_1-xN Heterostructures

Materials Research Society Symposium Proceedings 468, 237 (1997).

Below is the abstract submitted to the meeting, not the abstract of the published paper:
In order to get a physical insight about the gain mechanisms in GaN and Ga_xAl_1-xN alloys, we report on high density effects and optical gain measurements on samples grown with MOVPE. With temperature and excitation dependent photoluminescence (PL) the nonlinear properties of the band-edge luminescence is investigated. The intensity dependent spectra of the spontaneous emission are dominated by inelastic scattering processes of excitons (P-band) up to 180 K. At higher excitation densities we observe broadening and a red shift of the P-band, which can be explained by scattering of the excitons in the A$\_\{\{n\}^\{=2\}\}$ and A$\_\{\{n\}^\{-3\}\}$ state. In the spectral range of the donor bound exciton a broad band appears, which we assign to the recombination of biexcitons. Up to room temperature, the recombination of an electron hole plasma and the phonon-assisted recombination of excitons dominate the spectra. The gain maximum at low temperature is observed at the energy position of the P-band. Additionally, the (X-LO) luminescence clearly shows gain. At higher temperature, the spectral range showing gain is extended to the range between 3.1 eV and 3.8 eV, indicating that free carriers and the phonon-assisted excitonic recombination broaden the gain spectra. The results of GaN are compared with the Ga_xAl_1-xN alloys to study the influence of the increasing localization of carriers and excitons.

This paper is part of Gallium Nitride and Related Materials II

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