Characterization of Rapid Melt Growth (RMG) Process for High Quality Thin Film Germanium on Insulator

Abstract

Germanium is one of the most promising materials for high performance infra-red photovoltaic devices. High quality singlecrystal germanium on insulator structures can be produced by a Rapid Melt Growth process. Experiments show that thin-film germanium deposited by physical vapor deposition provides better quality in comparison with chemical vapor deposition. The longitudinal optical Ge-Ge peak in Raman spectrum is shifted from the expected 300.2 cm-1 position due to tensile stress resulting from the thermal expansion differences of the materials. The importance of silicon in the rapid melt process is confirmed by the fact that germanium films on sapphire substrates yielded polycrystalline structure. Films produced at high temperature (980 oC) show Ge- Ge Raman peak with linewidth of 3.3 cm-1 indicating good crystalline quality, comparable to bulk germanium (3.2 cm-1), and thus demonstrating the potential to produce low cost high quality germanium films.