| Summary: | 碩士 === 國立臺灣海洋大學 === 光電科學研究所 === 92 === The .optical properties of the type-II staggered ZnTe/ZnSe quantum dots(QDs) and CdTe/ZnTe quantum well(QW) coupled quantum dots(QDs) nanostructures were studied by photoluminescence(PL), time-resolved photoluminescence(TRPL) and photoluminescence excitation(PLE) measurements.
The PL and PLE spectra indicated the existence of the type-II staggered ZnTe/ZnSe QDs. It was found that the self-assembly QDs could split at certain thickness they were grown in order to relieve the built-up strain, and therefore, two categories of QDs with different averaged sizes were created. Two main peaks corresponding, to the two populations of the QDs with different sizes were found in the PL spectra. The temperature dependent PL spectra of the larger QDs showed peculiar behaviors by increasing the PL intensity with the increase in the temperature ranged between 50K and 90K, while that of the smaller QDs show the normal decrease in the PL intensity with the increase in the temperature. We found that the abnormal behavior for the larger QDs can be understood by assuming the existence of the defects near the larger QDs,. From the TRPL measurements, the comparisons of the lifetimes for the carriers in larger QDs and the smaller QDs supported the assumption and was able to explain the discrepancy in activation energies between the larger and the smaller QDs.
In the case of the CdTe/ZnTe QW coupled QDs, it was found that the full width of the half maximum(FWHM) of the PL spectra decreased and the intensity of the PL spectra increased as the separation larger between the QW and QDs were decreased. In additions, TRPL measurements, showed that the QW coupled QDs with the thinnest separation layer exhibited the shortest lifetime in PL decay process. We point out that all the phenomena can be understood by the effects of the strain induced by the ZnTe separation layer and the tunneling of carriers from QW to QDs in the QW coupled QDs nanostructures.
|
|---|
