| Summary: | 碩士 === 北台科學技術學院 === 機電整合研究所 === 94 === In this thesis, we have systematically investigated the carriers transferring characteristics of self-assembled InAs/GaAs quantum dot (QD) heterostructures through the measurements of temperature-dependent and power-dependent photoluminescence (PL).
The InAs QDs samples were carried out by metal-organic chemical vapor deposition system. The dot density, and dot size uniformity of the samples are different because of their different growth interruption (GI) time during the growth process. According to the measured results, we identify that the full width at half maximum (FWHM) and the peak energy of PL spectra are highly related to the GI time of InAs samples. For the sample with shorter GI time, thanks to the lower dot size uniformity, the FWHM decreases apparently with temperature, accompanied by a quick redshift of the peak energy. It is attributed to the carriers thermally activate outside the dots and redistribute among dots via the wetting layer. As the temperature increases further, the FWHM increases and quick-redshift of peak energy slows down because the electron-phonon scattering becomes important. For sample with longer GI time, which resulting in the better uniformity of this sample, the unusual decrease of FWHM is not observed in the measurement of the temperature dependent PL spectra. Considering the better uniformity of the sample, the effect of carrier redistribution on PL spectra is unapparent. Therefore, the FWHM increases gradually with temperature.
In the measurement of power-dependent PL spectra, the correlation between the carriers transferring and density of state (DOS) in QDs are discussed in depth. With lower incident excitation power, the lower filled portion of DOS leading to the evident carrier redistribution effect in QDs, thus the decrease of FWHM and the redshift of peak energy both increase with decreasing incident power. According to the measurement and analysis of the temperature-dependent and power-dependent PL spectra, the carriers transferring mechanism of QDs heterostructures is well explained and is expected to improve the design of optoelectronic devices.
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