Novel properties of nanostructured semiconductors

To have a complete understanding of nanostructured semiconductors, in this thesis we emphasize the strong correlation between morphological, structural, and optical properties. Besides the investigation of basic physical properties, several methods have been developed to enhance optical properties of nanostructured semiconductors, and the corresponding mechanisms have also been established. In addition, the technique of selective wavelength mapping for the characterization of nanomaterials based on conventional cathodoluminescence (CL) has been developed. The studied nanomaterials include SiOx nanoparticles, ZnO nanowires, CdS nanoparticles, AlGaN epifilms, and self-assembled InAs quantum dots. Photoluminescence, energy dispersive X-ray spectrum, cathodoluminescence were employed to explore the band and defect emissions, compositions, and relations among them. Several methods have been designed to suppress or enhance luminescence properties. For SiOx nanoparticles, a kind of MCM-41 mesoporous, embedding of gold nanoparticle can greatly enhance the defect emission by one thousand times. It is discovered that second harmonic surface plasmon resonance can be used to enhance optical properties of nearby nanomaterials. For CdS nanoparticles, Au-CdS core-shell nanostructures reveal 40 times enhancement in the emission intensity. For ZnO nanowires coated with metal nanoparticles, we found that the defect emission can be suppressed to the noise level, while the band gap emission can be greatly enhanced. The intensity ratio of the band gap and defect emissions can be improved by up to one thousand times. Surface plasmon resonance induced energy transfer in nanocomposites is used to interpret the giant enhancement. With the newly developed CL image technique, direct evidence of the compositional pulling effect in AlGaN epifilms shows gradual variation of Al along the growth direction. Finally, self-assembled InAs quantum dots reveal various properties with different spacer layer. The dot sizes are strongly correlated with the stain induced by the spacer layer.