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Electron-Hole Plasma Mott Transition and Stimulated Emission in GaN
K. KYHM,B. BEAUMONT,J. F. RYAN,P. GIBART,R. A. TAYLOR 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
We present femtosecond pump-probe re ectance measurements of excitons in GaN for various pump intensities. Saturation of the excitonic absorption with increasing carrier density has been measured in the case of resonant and non-resonant excitations during the rising times, and the exciton bleaching densities for various excitation energies have also been measured. We found that the resonant excitons are bleached at higher densities (10 times) than the non-resonant excitons due to the absence of free carriers. The stimulated emission mechanism is investigated by measuring simultaneously the photoluminescence and the time-resolved re ectance near the band edge, over a range of excitation densities. The onset of the stimulated emission coincides with the bleaching density of the non-resonant excitons as well as a theoretical gain threshold density. These results suggest that the stimulated emission in GaN is due to the electron-hole plasma.