Raman and XRD studies of Ge nanocrystals in alumina films grown by RF-magnetron sputtering

Germanium (Ge) nanocrystals (NCs) embedded in alumina thin films were produced by deposition on fused silica and silicon (111) substrates using radio-frequency (RF) magnetron sputtering. The films were characterised by both Raman and X-ray diffraction (XRD) spectroscopy. The deposition conditions were optimised in order to obtain crystalline Ge nanoparticles. In as-deposited films, the typical NC size was ∼3 nm as estimated by means of X-ray diffraction. Raman spectra taken from as-deposited films revealed both amorphous and crystalline semiconductor phases. Annealing was performed in order to improve the crystallinity of the semiconductor phase in the films. After a 1 h annealing at 800 °C the mean NC size estimated from the XRD data and Raman spectra increased to ∼6.5 nm. An increase in the crystallinity of the Ge phase was also confirmed by the Raman spectroscopy data.