Preparation And Properties Of Multilayer Germanium Nanocrystals And Cuprous Oxide Film

The thesis includes two parts. In the first part, we have studied the fabrication and characterization of multilayered Ge nanocrystals (Ge-ncs) with high density and better uniformity in size and distribution which were prepared by superlattice method, using a rf magnetron co-sputtering technique and subsequent annealing in N2ambient. Sputterings were carried out using (Ar+02) and (Ar+N2) gas, respectively. The optical properties of the prepared Ge-ncs were investigated using spectroscopic ellipsometry. In the second part, we have prepared the cuprous oxide (Cu2O) film photovoltaic materials and studied the structural properties and photoluminescence spectrum of the prepared Cu2O film by x-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectrum measurement (PL). In this thesis, we have obtained the following conclusions:1. Annealing has an important influence on the structure of multilayered Ge-ncs. Higher annealing temperature and longer annealing time are adverse to the growth of Ge-ncs. For preparing the multilayered Ge-ncs (The area ratio of Ge on the composite target was11.2%.), the best annealing condition is550℃,60min; For preparing the multilayered Ge-ncs (The area ratio of Ge on the composite target was11.2%.), the best annealing condition is750℃,30min.2. The multilayered Ge-ncs (The area ratio of Ge on the composite target was8.4%.) embedded in Si and Ge oxide were prepared using (Ar+02) gas. The size of the Ge-ncs is9.8nm. The refractive index n(X) showed a normal dispersion and the extinction coefficient k(k) indicated a bigger absorption characteristic around1340nm;3. As compared with bulk Ge, the multilayered Ge-ncs (The area ratio of Ge on the composite target was8.4%.) exhibited a certain blue shift in the absorption spectrum and a band gap expansion of0.16eV. The band gap expansion was discussed in terms of quantum confinement effect as well as the sp3tight binding model;4. The multilayered Ge-ncs (The area ratio of Ge on the composite target was8.4%.) embedded in SiOxGeNy were prepared by a (Ge+SiO2)/(SiOxGeNy) superlattice method, using (Ar+N2) gas. The size of the Ge-ncs is5.4nm.. The refractive index n(λ) showed a normal dispersion and the extinction coefficient k(λ) indicated a bigger absorption characteristic around720nm;5. The optical band-gap energy of the prepared multilayered Ge-ncs (The area ratio of Ge on the composite target was8.4%.) embedded in SiOxGeNy matrix was determined to be1.89eV. The absorption spectrum shows considerable blue shift compared with that of bulk Ge, which is ascribed to the quantum confinement effect in Ge-ncs;6. For preparing CU2O film, the best experimental condition is to immerse pure copper plates in10-1M CuCl2during24h. The size of the prepared CU2O microcrystals with good uniformity can be2.5um;7. The observed PL peak centered at510nm and540nm are both attributed to the the band gap transition.