22 June 1998 Large optical nonlinearities in the bandgap region of GaN thin films grown by MOCVD on sapphire
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Proceedings Volume 3419, Optoelectronic Materials and Devices; 341909 (1998) https://doi.org/10.1117/12.310991
Event: Asia Pacific Symposium on Optoelectronics '98, 1998, Taipei, Taiwan
We report the results of nanosecond non-degenerate optical pump-probe experiments and single-beam power dependent absorption experiments performed on metalorganic chemical vapor deposition grown GaN thin films. Changes in the optical transitions near the band gap due to excess photo- generated free carriers were studied as a function of excitation density at 10 K and room temperature using pump- probe spectroscopy. At 10 K, strong, well-resolved features are present in the absorption spectra corresponding to the 1s A and B free exciton transitions. These features are shown to broaden and decrease in intensify due to the presence of the high densities of photo-excited free carriers generated by the pump beam, resulting in extremely large values of induced transparency, exceeding 4 X 104 cm-1 as the excitation density (Iexc) approaches 3 MW/cm2. In addition, large values of induced absorption are observed with increasing pump density in the below-gap region where gain was expected. This induced absorption was also found to be extremely large, exceeding 4 X 104 cm-1 as Iexc was increased to over 3 MW/cm2. At room temperature the resulting induced transparency and induced absorption were found to approach 2 X 104 cm-1 as Iexc approached 3 MW/cm2. The single-beam power dependent absorption experiments show enhanced bleaching of the excitonic transitions with increasing Iexc compared to the pump-probe experiments, while the below-gap induced absorption is drastically reduced in the single-beam experiments. The large values of induced transparency/absorption observed in this work and the fact that excitons have been shown to persist to over 450 K in GaN1 suggest the possibility of new opto-electronic applications for the group III nitrides.
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Theodore J. Schmidt, Yia-Chung Chang, Jin-Joo Song, "Large optical nonlinearities in the bandgap region of GaN thin films grown by MOCVD on sapphire", Proc. SPIE 3419, Optoelectronic Materials and Devices, 341909 (22 June 1998); doi: 10.1117/12.310991; https://doi.org/10.1117/12.310991

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