As Si technology is reaching its limits in solar cell and transistor applications, ways to improve these devices are being investigated. This study looks at the fabrication process of SiGe/Ge core-shell nanowires (NWs). Larger SiGe column structures can be oxidized to reduce their size and create a SiGe/Ge core-shell structure with a layer of SiO2 on the outside.
Initially, SiGe dry oxidation was investigated in epitaxially grown SiGe films with 15% and 20% Ge, focusing on the Ge pileup region to be used as a "shell" when nanostructured. The Ge pileup region was found by RBS to have between 57 and 65% Ge for the SiGe sample with 20% Ge, and between 34 and 44% for the sample with 15% Ge. The thickness of the pileup region was found to be linearly dependent on the oxide thickness, and independent of the Ge concentration. Ge was found near the top of the SiO2 layer in some of the oxidized SiGe samples.
Magnetron sputtering was used to get a supply of cheaper SiGe films,but these films were found to be amorphous and contaminated by oxygen.Further, the samples were patterned using photolithography, oxidized and characterized.
In addition, electrical characterization of Si nanocrystals embedded into a SiO2 matrix, resembling the core of NW structures after longer oxidations, was done. The samples show diode characteristics, exhibiting, however, large leakage currents and poor ideality factors. CV measurements show a significant deviation from the ideal MOS capacitor.