Correlation between oxygen distribution and luminescence efficiency in SiGe/Si layer structures measured by cathodoluminescence imaging and spectroscopy
SiGe layers and quantum wells grown on Si by low-pressure chemical vapour deposition (LPCVD) have been investigated by cathodoluminescence (CL) imaging and spectroscopy. Monochromatic imaging of the shallow bound exciton luminescence from the SiGe layers showed that in some cases it was not uniform. Dark regions were observed with dimensions mainly in the range 100 - 200 . As the density and size of these regions increased, the overall luminescence efficiency decreased. In this paper we report an investigation of the possibility that oxygen incorporation in the SiGe layer structures is responsible for the decrease in luminescence efficiency. Luminescence systems created in Si by radiation damage, known to be associated with carbon - oxygen and carbon - carbon complexes, were used to investigate the depth and spatial distribution of oxygen. A SiGe sample which contained a high density of dark regions was shown to have a high oxygen concentration close to the interface, either in the Si buffer layer or the substrate. Monochromatic CL images showed that the oxygen distribution was non-uniform, and that the areas where the oxygen concentration increased could be correlated with the regions where the shallow bound exciton luminescence efficiency decreased. This implies that oxygen incorporation in the SiGe layers during growth creates the non-radiative regions.