Optical and electronic characteristics of germanium quantum dots formed by selective oxidation of SiGe/Si-on-insulator

Germanium quantum dots embedded in a SiO₂ matrix fabricated by selective oxidation of SiGe-on-insulator structure were examined by high-resolution transmission electron microscopy, cathodoluminescence spectroscopy, and spectroscopic ellipsometry. The dot size and crystallite morphology were strongly dependent on thermal oxidation conditions. Visible photoemissions from Ge dots were observed at room temperature and they exhibited pronounced blueshifts of peak energies with increasing oxidation time, which can be correlated to the change in dot size, shape, or crystalline structure transition. The extracted refractive index of Ge dots examined by spectroscopic ellipsometry is lower than that of bulk Ge, which is also correlated to the nanocrystal size effects.