Annealing effects on the bonding structures, optical and mechanical properties for radio frequency reactive sputtered germanium carbide films

The effects of thermal annealing in vacuum on the bonding structures, optical and mechanical properties for germanium carbide (Ge-1 C-x(x)) thin films, deposited by radio frequency (RF) reactive sputtering of pure Ge(1 1 1) target in a CH4/Ar mixture discharge, are investigated. We find that there are no significant changes in the bonding structure of the films annealed below 300 degrees C. The fraction of Ge-H bonds for the film annealed at temperatures (T-a) above 300 degrees C decreases, whereas that of C-H bonds show a decrease only when T-a exceeds 400 degrees C. The out-diffusion of hydrogen promotes the formation of Ge-C bonds at T-a above 400 degrees C and thus leads to a substantial increase in the compressive stress and hardness for the film. The refractive indices and optical gaps for Ge-1 C-x(x) films are almost constant against T-a, which can be ascribed to the unchanged ratios of Ge/C and sp(2)-C/sp(3)-C concentrations. Furthermore, we also find that the excellent optical transmission for an antireflection Ge-1 C-x(x) double-layer film on ZnS substrate is still maintained after annealing at 700 degrees C. (C) 2008 Elsevier B.V. All rights reserved.