Versatile and Quantitative Spectrometer of Nonradiative recombination centers by Using Two-Wavelength Excitation method

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We exemplified the following research results during the project :(1)By combining a tunable below-gap excitation source (Optical Parametric Oscillator) and a sensitive CCD camera etc., we realized more versatile system of two-wavelength excited photoluminescence(TWEPL) for wider materials.(2)Inserting buffer layers with sufficient thickness, increasing quantum-well periods and utilizing modulation-doping were found to be effective for improving light emission efficiency through the characterization of GaN/AlGaN quantum wells grown by plasma-assisted MBE in Hannover University (Germany) and by our MOCVD technique.(3)We observed directly the formation of a trap-level due to an UV light irradiation during the measurement. The BGE effect after the trap formation was explained well by our two-levels model.(4)First detection of nonradiative centers in an InAs quantum dot has been done. Its temperature dependence is important for analyzing carrier dynamics in the quantum dot. In addition, a new trap level in a Y_2O_2S:Eu phosphor was resolved clearly by combining TWEPL with thermo-luminescence technique.Thus our TWEPL spectrometer became a versatile way to characterize belowgap states in wider range of light emitting materials.