Abstract
According to Moore’s law, the number of transitors on a computer chip would double every 18~24 months. Therefore, in order to achieve the goals of high operation speed and high device density, semiconductor industrials keep downscaling the size of MOSFETs. However, the reduction of device size would approach the limit of top down technology, therefore the method of synthesis one-dimensional (1D) semiconductor nanostructures is of particular interest because of their potential applications in nanoscale electronic and optoelectronic devices. First, in order to grow Si nanowires without the contamination of gold catalysts, we used the method of OAG mechanism and we found two critical growth factors : (1) temperature gradient and (2) a pressure smaller than 1 atomosphere. From investigation of TEM images, we found the Si nanowire is core-shell structure with single crystalline Si core and amorphous silicon oxide shell. On the purpose of growing Si nanowires with controllable dimensions, we tried to find the relationship between the process parameters and nanowire’s diameters. At the same carrier gas flow rate, the average diameter of Si nanowires increases with the ambient pressure and the density of Si nanowires decreases with the ambient pressure. When we fixed the ambient pressure, we found that the average diameter of Si nanowires increases with the flow rate of carrier gas. We also discovered that the Si nanowires prefer to nucleate at the sites of cracks or defects first, which are energetically unstable. When we decreased the temperature of SiO powder to 1050℃ and gold-coated Si substrate to 620℃, we could synthesize pure Ge nanowires. The Ge nanowire is core-shell structure with single crystalline Ge core and amorphous GeOx shell. The diameter of Ge nanowires increases with the ambient pressure as well. Finally, by adding the iodine pellet(I2) into the alumina tube, we successfully synthesized the Si1-xGex nanowires by the method of simple thermal evaporation of SiO and Ge powder. This method is nontoxic、low cost and it can synthesize large amount of Si1-xGex nanowires on Si substrate at a time. In this thesis, we proposed the growth mechanism as well. The Si1-xGex nanowire is single crystal and its growth direction is [110] with Ge ranging from 3.70% to 17.76%.