Exciton Process In Zncdse Quantum Well / Cdse Quantum Dot Composite Structure

Low dimensional II- VI semiconductor structure is one of ideal material for exciton nonlinear optical devices at room-temperature and greem-blue emission devices due to it's large exciton binding energy and strong room-temperature exciton effect. Thus the excitonic effects in II- VI semiconductor quantum wells and asymmetric double quantum wells have been studied deeply and widely. However, the studies on the exciton process in self-assembly quantum-dots / quantum well complex structure have been carried out just in recent years. Such novel structure reveal peculiar properties.In this thesis, the femtosecond pump-probe experiment system was set up to investigate the exciton tunneling between CdZnSe qutantum well and CdSe quantum dots, Micro-Raman,Raman and photoluminescence with temperature were measured on the CdSe quantum dot and CdZnSe QWs/CdSe QDs complex structure. The main experimental results and conclusions presented in this thesis are summarized as follows 1 . Femtosecond pulse pump-probe experiment system was established with two mode(monochromatic transmission, white light transmission), wavelength formonochromatic mode can be adjusted ranging from 350nm to 650nm. Thewavelength of pump light in white light mode is 400nm.2. The excitonic tunneling from CdZnSe QW to CdSe quantum dots under resonant excitation was investigated using femtosecond pump-probe technology on the CdZnSe quantum well/CdSe quantum dots structure. The exciton lifetime in quantum well is up to 1.8 ps under the thickness of ZnSe barrier layer lOnm. We found that the exciton transference between CdZnSe quantum well and CdSe quantum dots is dominated by exciton tunneling at a thin ZnSe barrier layer. However, with thickness of ZnSe barrier increasing, mechanism of the exciton transference process changed .3. Micro-Raman and photoluminescence studies of CdSe quantum dots have been carried out under different temperature. We studied the phonon mode of CdSe QDs by Raman spectra, and estimated the energy of LO phonon in CdSe QDs located in the range from 215-235cm"'. The exciton-phonon coupling in CdSe QDs and its wetting layer were investigated by PL dependent of temperature. From comparison of coupling in the two parts, we found that the exciton-LO phonon coupling was restrained in CdSe QDs.4. Photolumescence and micro-photoluminscence of CdZnSe QW/ZnSe/CdSe QDs with different ZnSe barrier thickness was studied to investigate the influence oftunneling on excitonic combination in quantum well and quantum dots. We studied the temperature dependent of the excitonic recombination.