Characterization of Ge nanocrystals in a-SiO2 synthesized by rapid thermal annealing

We report the synthesis of nanocrystals of Ge embedded in a-SiO2 matrix by rapid thermal annealing (RTA). The films were deposited by rf-magnetron co-sputtering of Ge and SiO2 followed by RTA for 300 s. Raman studies indicate a transition of Ge from amorphous to nanocrystalline form when annealed between 700 to 800 degrees C. The Raman spectra were analysed in terms of phonon confinement model and the estimated nanocrystal size was between 20 to 80 Angstrom. A strong visible broad band photoluminescence was observed for the crystal size between 20 to 60 Angstrom. The photoluminescence showed a blue shift with decrease in the nanocrystal size. The origin for the photoluminescence is discussed in terms of quantum confinement of excitons. (C) 1999 Elsevier Science B.V. All rights reserved.