Optical Properties of Multilayered Ge Nanocrystals Embedded in SiOx GeNy Thin Films

Multilayered Ge nanocrystals embedded SiOxGeNy thin films have been prepared by the (Ge+ SiO2/(SiOx GeNy) superlattice method, using the radio frequency (rf) magnetron co-sputtering technique and subsequent annealing. X-ray diffraction (XRD) meaurement indicated the formation of Ge nanocrystals with an average size of 5.4 nm. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (Ge+ SiO2) layers. This superlattice technique significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the 'Z' growth direction. Optical properties of the prepared Ge nanocrystals have been investigated by spectroscopic ellipsometry (SE) and their optical band-gap energy is determined to be 1.92 eV. Absorption spectra of the prepared Ge-ncs shows considerable blue shift compared with bulk Ge, which is ascribed to quantum confinement effect in the Ge nanocrystals.