The Formation And Characterization Of ZnCdSe Quantum Dots

As one portion of nanotechnology, semiconductor quantum dot (QD) structures are of great importance not only in resolving base physical problems but also in realizing practical applications. Therefore, the research on QD is very significant both in academic and application point of view. In this thesis, aiming at the hotspots in QD, we deal mainly with the growth and characterization of ZnCdSe QD structures, and the major fruits are listed below:1. The ZnCdSe/ZnSe QD structures were prepared in Stranski-Krastanow (S-K) mode by metalorganic chemical vapor deposition (MOCVD) technique. Prior to the growth, the critical thickness, which plays a vital role in the formation process of QD, is numerically calculated in terms of the strain relaxation, and the growth is carried out under the guidance of the calculated results. The successful preparation of ZnCdSe QD on ZnSe provides a way for the fabrication of QD in S-K mode with relative small lattice mismatch. In addition, ZnSeS QD were prepared in Volmer-Weber (V-W) mode on lattice match substrate, and the formation process of the dots was investigated as well.2. Based on the theory that the optical properties of ZnCdSe/ZnSe QD structure at different formation and ripening stage are different from each other, by investigating the variation in emission peak energy and integrated intensity, the formation and ripening information of the dots was obtained, which overcomes the disadvantage of atomic force microscopy (AFM) in that it can not be applied to the measurement of the initial formation stage of the QD. Furthermore, it is of great help to clarify the controversies in the ripening process of Se-compound QD.3. In some occasions, the dependence of the integrated photoluminescence (PL) intensity of QD structures on temperature is not monotonic. That is, the PL intensity increases firstly and then decreases with increasing temperature.Referring to the formation process of QD, it is accepted that there formed a groove around the dot during the formation process due to mass-transfer. When the dots were capped by a compound with larger band gap, there will appear a potential maximum due to larger confinement. The maximum will prevent the carriers from entering the dot, and the origin of the kink point is resulted from the prevention.