Optical properties of InAs/GaAs quantum dots with InGaAs overgrown layer

• Main Authors: Chang-Kang Wang, 汪長剛
• Other Authors: J. L. Shen
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/24917488314115983537

碩士 === 中原大學 === 應用物理研究所 === 93 === Abstract We study the optical properties of self-organized InAs/GaAs quantum dots (QDs) and InAs/GaAs QDs with InGaAs overgrown (strain-reduced) layers by using photoluminescence (PL). A rich fine structure in the excited states of confined excitons were observed in photoluminescence excitation (PLE) measurements, indicating the quantum-size effect of exciton transitions in InAs/GaAs QDs. The strain relaxation due to the InGaAs overgrown layer was demonstrated by measuring the energy spitting of the heave-hole and light-hole in wetting layers. We also studied the temperature dependence of the PL decay times of InAs/GaAs QDs by time-resolved photoluminescence (TRPL). It is found the decay times first increase with increasing temperature up to ~ 150 K, then decrease at higher temperatures. The increased decay times can be explained by the thermal redistribution of electron-hole pairs from quantum dot states into the wetting layer followed by recapture. The effect of the thermal redistribution is more pronounced in the InAs/GaAs QDs with InGaAs overgrown layers. The decay-time decrease at higher temperatures is attributed to nonradiative recombination. By using a 976- nm laser with the photon energy smaller than the wetting-layer energy, an extra decay time of PL was observed. The dependence of the extra decay time on temperature was also investigated. The decay times first increase with increasing temperature and show two maxima (50 K and 150 K) as a function of temperature. The initial increase of PL decay times has been attributed to the thermally induced redistribution of the photoexcited carriers among the ground state and the first excited state in InAs/GaAs QDs.