Raman and photoluminescence properties of Ge nanocrystals in silicon oxide matrix

Ge nanocrystals (nc-Ge) embedded in silicon oxide thin films have been fabricated using rf magnetron co-sputtering deposition and post-growth thermal annealing method. Raman scattering and photoluminscence (PL) measurements have been used to characterize their crystallization and light emission properties. The Ge crystallinity and nanocrystal size obtained using a three-peak fitting method based on a phonon confinement model have been found to increase with the increase of annealing temperature. The observed blue photoluminescence band located at ∼3.1 eV and a weaker band at ∼2.4 eV under the excitation of 325 nm laser did not show significant size dependence while their relative intensities were related to the addition of H2 or O2 into the sputtering ambient. The photoluminescence mechanism is discussed.