Fabrication and Characterization of ZnSe Quantum Dots

• Main Authors: Liao, Ming-Chih, 廖明智
• Other Authors: Chang Yen-Huei
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/64254840041796975981

博士 === 國立臺灣大學 === 物理學系 === 85 === In this study, a new method for quantum dotsfabrication was propsed and successfully demonstrated.Rather than Stranski- Krastonov mode, quantum dots canalso be grown under Volmer-Weber mode. Both Si and GaAs,two popular and commertially available substrates,were used. Despite the crystal quality of the uantumdot structure on both substrates was very different, theperformance in optical measurements wasthe same. Thissuggests that the presence of defects may not affect the carriers in the quantum dots.In this study, ZnSe and ZnS were used as the well and the barrier material. The average observed size of the quantum dots was about 100 A, as measured by atomicforce microscopy (AFM), high resolution scanning electron microscopy (HRSEM), and high resolutiontransmission electron microscopy (HRTEM). Anomalous straincondition was found in the quantum dot structures. Itsuggests that strain in nanostructures might be different from those in larger scales. Ripening effectwas found both in AFm and photoluminescence (PL). It is the first PL observation of the ripening effect. Thevariation of PL spectrum suggests the ripening processstablized in about one month after growth.Strong carrier confinement was also observed in PLstudy. The emission persisted up to room tempreature. Itis an indication of stronge excitonic effect in the quantum dot structures. In the temperature dependence PLmeasurements, exciton binding energy was found to increase with decreasing dot size. It was shown that the increasement can be five times the bulk value. In the measurement of PL power dependence, the integrated PL emission was found to be linear, or superlinear, to the excitation power. The superlinear feature wuggests thatradiative recombination processes dominates.The PL emission showed no differences by above and below barrier excitation. Therefore carrier capture inthe quantum dots might be very strong. From the time-resolved PL measurement, the recombination lifetime wasfound to be larger than that of quantum wells. IT isanother evidence that liggle non-radiative channelsinvolves in the recombination processes. Another fastdecay component was also resolved from the decay curve.It was attribured to higher energy state emissions.Bandfilling at normal excitation level was observed inthe quantum dot system.