Physical properties of thin GeO2 films produced by reactive DC magnetron sputtering

We have studied optical and structural properties of GeOx films produced by reactive DC magnetron sputtering of Ge targets in an Ar/O-2-mixture. Optic al spectroscopy measurements of reflectance and transmittance of the films were employed to determine optical properties. The film structure was deter mined by X-ray diffraction measurements, while X-ray reflectometry was used to determine the thickness, density, and roughness of the films. The him t opography was additionally characterized by atomic force microscopy. For ap propriate oxygen flows highly transmitting GeOx films can be grown at rates up to 3 nm/s for power density of 2.6 W/cm(2). Optical and structural prop erties of the films are closely correlated and can be controlled by the oxy gen dow. With increasing oxygen how an increasing growth rate of the oxide films is initially observed. The resulting films above 20 seem and below 25 seem O-2 are transparent in the visible range, have a negligible roughness and are amorphous. A further rise in oxygen how lends to a pronounced decr ease in growth rate above 25 seem and a further increase in the bandgap of the germanium oxide up to mon than 48000 cm (1) (5.95 eV). This transition in him growth is accompanied by an increase in roughness and a structural t ransition leading to polycrystalline films of alpha-GeO2 (quartz-structure) . Nevertheless, the film density is hardly affected by the structural chang e and remains rather constant around 3.65 g/cm(3), which is 85% of the dens ity of single crystalline alpha-GeO2. A model is presented which can accoun t for the change of film properties. (C) 2000 Elsevier Science S.A. All rig hts reserved.