Growth of high quality amorphous silicon films with significantly improved stability

Abstract

We report on the results of a systematic series of experiments aimed at improving the stability of amorphous silicon (a-Si:H) films. We find that very low levels (0.2–0.4 ppm) of compensation by boron, when combined with growth conditions that favor a robust microstructure in the material, results in films with significantly improved stability and very low defect density. The films were grown using a reactive plasma beam technique using a remote plasma beam from an electron-cyclotron-resonance source. The improvement in stability is seen under both short-term (a few minutes) light soaking, and also under light soaking under high intensity (10×sun) illumination conditions. We conclude that the improvement in initial stability is a result of compensation of native donors (probably oxygen) in the material by boron. The surprising reduction in long term instability and corresponding defect density upon compensation implies that the microstructure and structural changes around the native impurities may play a role in the long-term instability of the material.