Optical property investigation of SiGe nanocrystals formed by electrochemical anodization

We report on the optical property investigation of SiGe nanocrystals (NCs) prepared by electrochemical anodization (ECA) of SiGe layer grown by ultrahigh vacuum chemical vapor deposition (UHVCVD). At room temperature, SiGe NCs with higher Ge content demonstrate a redshift of the photoluminescence (PL) peak compared to Si NCs. It was found that the surface chemical composition, density, and the size of the SiGe NCs were very sensitive to the annealing conditions. Various spectroscopy measurements such as PL, FTIR, and XPS have been carried out to reveal the mechanism of the PL peak transition. The results indicated that the PL peak position was determined by two major factors, namely, interface state density and the size of SiGe NCs. It was shown that the higher the interface state density, the more significant the redshift of the peak position. While the smaller the size of the SiGe NCs, the more significant the quantum size effects become, resulting in the blueshift of the PL peak position.