Light induced degradation of amorphous silicon containing nanocrystalline silicon

The effect of light soaking (LS) is studied in hydrogenated amorphous silicon (a-Si:H) containing different amounts of nanocrystals, prepared by varying the deposition conditions in a plasma enhanced chemical vapor deposition (PECVD) system. We find that the presence of nanocrystals (nc-Si) stabilizes the a-Si:H against LS. The long range potential fluctuations (LRPF) are measured and we find that they become smaller as the fraction of nanocrystals (χ) in the films increases. Raman spectra show a peak at 490 cm−1, which is taken to be the result of Intermediate Range Order (IRO) in the films. This IRO peak appears just when the hydrogen dilution is sufficiently high for the crystallization to begin, and increases with increasing hydrogen dilution as the crystallization increases. In contrast LRPF have maximum width when χ is zero and it decreases as χ increases. Further, the degradation upon LS is negligible when χ > 25%. We suggest an alternative mechanism for the improved stability, in which the photogenerated carriers moving under the influence of the long range potential fluctuations have a propensity to go to nc-Si, and recombine in that region.