Growth Research And Infrared Optical Properties Of Sn Quantum Dots

Quantum dots (QDs) have great electrical, optical properties and wide potential applications on nano-electronics, opto-electronics and quantum calculation in future. In 1997, Nakajima et al. had formed Sn QDs in SiO2/Si by low energy ion implantation. The study on Sn QDs has become a hotspot now. There are two states of Sn QDs:α-Sn QDs andβ-Sn QDs. The narrow bandgap ofα-Sn is expected to increase significantly as the particle size decreases because of its very small effective mass (0.0236 m0). Metallicβ-Sn nanocrystals have been proposed as charge storage elements as they offer a higher density of states around the Fermi level and more uniform charging characteristics than semiconductor nanocrystals. The incorporation of Sn in Si in terms of small Sn precipitates may lead to a direct and tunable energy gap. Up to now, lots of studies have been made on photoluminescence and infrared absorption of Sn QDs. However, the surroundings of Sn QDs are so complicated that consistent conclusion hasn't been made.In this thesis, we have synthesized high density of Sn QDs on pure Si(001) substrate by SPE. The dependence of the morphology and crystallinity of Sn QDs on Sn coverage, annealing temperature and annealing time was investigated. From the Raman spectra of Sn QD samples, we can clearly see the Raman peaks ofα-Sn thin film andα-Sn QDs, as well as the upward shift of the Raman peak due to the large residual strain inside Sn QDs. However, the phase of Sn QDs will transform toβ-Sn whether increasing annealing temperature or prolonging annealing time. Due to the large size of Sn QDs, their characteristic absorption peaks were not observed from the synchrotron FTIR spectra.In addition, ZnO QDs have superior optical properties compared with bulk crystals. With the effect of quantum confinement, the PL peak of ZnO QDs will make an upward shift to near ultraviolet and find applications on ultraviolet luminous emission devices. In our experiment, we studied the quantum confinement effect of ZnO QDs. This work is supported by the Ministry of Education through doctoral innovative project of synchrotron radiation (No 20090655S).