Raman and electron microscopic studies of Si1-xGex alloy nanowires grown by chemical vapor deposition

Si1-xGex alloy nanowires (SiGeNWs) were grown by Au-catalyzed chemical vapor deposition and studied by Raman spectroscopy, transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDS) in TEM (TEM-EDS). The relationship between the growth parameters and the structure of the SiGeNWs was clarified by systematically changing the growth conditions over a wide range. Raman and TEM-EDS results demonstrated that the SiGeNWs consist of a lower Ge composition core and a higher Ge composition shell epitaxially grown on the surface of the core. The effects of oxidation on the structure of the SiGeNWs were studied. It was found that oxidation leads to segregation of the Ge atoms at the interface between the SiGeNWs and SiO2, which in turn results in a large inhomogeneity in Ge composition. Oxidation at a very low rate in a diluted oxygen gas atmosphere is required to avoid the formation of Ge particles and minimize the inhomogeneity.