Abstract
AbstractThe fabrication and characterization of semiconductor nanostructures, such as quantum wells, wires and dots, are of great interest because of their potential applications in the electronic and optoelectronic quantum devices. In recent years, there have been an enormous amount of studies aimed at the realization of the Si1-xGex alloy nanostructures. By changing the Ge content, the physical and chemical properties of this alloy, like band gap and melting point, may be adjusted. In this study, Si1-xGex nanoparticles were prepared by a thermal evaporation system. Unlike traditional approaches in preparing Si1-xGex quantum dots, such as self-assemble and co-sputtering, an inert-gas evaporation was employed to fabricate isolated nanoparticles without any film effects.The particle size distribution and crystallinity of the nanoparticles were determined both by XRD and TEM. EDX and ICP measurements were made to analyze the composition distribution. The optical properties were examined by UV-visible transmission spectroscopy and photoluminescence spectroscopy.From the TEM images, all particles were spherical, and increasing of the working pressures led to increased particle size. The XRD patterns showed broad peaks for every sample. Besides, the XRD peaks position were shifted toward the Ge-rich region (~27.2o) as the working pressure increased, which was ascribed to the retardation effect of Ar atoms. The Si atom was easier to be retarded by Ar atom than Ge. According to the EDX results, the nanoparticles prepared at low working pressure (~1torr) had a wide composition distribution, because the collision frequencies were not high enough for Si and Ge atoms to form complete solid solution. Even for higher working pressures, the composition of the nanoparticles was not uniform.In addition, the UV-visible spectra showed red shift of the absorption edges. The absorption edge was shifted from 380nm to 540nm which is between the absorption edges of the pure Si and Ge nanoparticles, respectively. The PL spectra also revealed a red shift tendency as the Ge content increased. Therefore, the Ge doping can change the band structure and optical properties of nanocrystalline Si.