Characterization of semiconductor quantum dots

The applications of various optical and electrical characterization techniques to the study of semiconductor quantum dots (QDs) are summarized. Photoconductivity enhancement effect in CdS-PVK nanocomposite is studied by optical absorption, photoluminescence (PL), photoconductivity spectroscopy, and time-resolved PL. It is found that the photoconductivity of the composite is greatly enhanced in comparison with that of a simple mixture of CdS nano-particles and PVK. PL spectra have shown that luminescence from PVK is dramatically quenched by the incorporation of a low density of CdS particles. Time-resolved spectra reveal that the decay of the PL from the dots of the composite is much longer than that in the simple mixture, These have been attributed to a fast carrier transfer mechanism between CdS QDs and PVK matrix. In addition, optical properties of PVP-capped ZnO QDs are investigated in details. Typical PL spectra of PVP-capped ZnO QDs consist of a sharp UV peak located at about 3.45 eV and a broad green emission band centered at 2.34 eV. At certain Zn²⁺/PvP ratios the green emission band is quenched and only strong UV emission remains. This effect is attributed to the surface modification of ZnO quantum dots with PVP. We are able to associate the UV emission from ZnO QDs to localized states by applying temperature and excitation power dependent PL. Finally, the electronic level of molecular beam epitaxy grown self-organized ZnSe QDs embedded in ZnS is determined by applying PL, capacitance-voltage measurement, and deep level transient spectroscopy.