High‐temperature diffusion barriers from Si‐rich silicon‐nitride

By radiotracer diffusion experiments, it is shown that the 31 Si diffusivity in Si‐rich nonstoichiometric amorphous silicon‐nitride layers (Si 3+ x N 4− x ) sharply drops to low values at a temperature of 1075 °C and is unmeasurable at lower temperatures. A similar behavior was found for Au and Ge diffusion in Si 3+ x N 4− x , however, at lower temperatures. Utilizing this diffusion‐blocking effect, thin films of Si 3+ x N 4− x were employed as efficient diffusion barriers for preventing the diffusion of Fe and other constituents from a steel substrate into a Cu(In,Ga)Se 2 absorber layer of a thin‐film solar cell. The reduced diffusion consequently allows the employment of higher process temperatures, which can lead to larger grains and an improved cell performance. Copyright © 2006 John Wiley & Sons, Ltd.