Germanium nanoclusters in silica thin films

We have characterized the properties of Ge nanoclusters in silica films. The films are grown by physical vapor deposition (PVD) or ion-beam-assisted deposition (IBAD): by co-deposition of Ge and SiO2 with and without the presence of an argon ion beam. The IBAD process affects the development and ultimate morphology of the nanoclusters. Rutherford backscattering (RBS) and index of refraction measurements give the volume fraction of Ge nanoclusters in the silica films and quantify the effects of sputtering on the ultimate film composition. At a Ge/SiO2 arrival rate greater than or equal to 0.8, SiO2 is preferentially sputtered; at lower arrival rates Ge is preferentially sputtered. Absorption measurements are used to deduce the effective band gap of the Ge nanoclusters and the growth of the nanoclusters with annealing. X-ray diffraction studies and transmission electron microscopy confirm that the IBAD processing accelerates the growth of the Ge nanoclusters at low annealing temperatures and inhibits the ultimate size of the nanoclusters, as compared to clusters in those films grown by PVD. Photoluminescence of the Ge-silica films is examined for the IBAD and PVD cases.