Effect of light soaking on CPM absorption spectra in silicon films with mixed amorphous‐nanocrystalline structure

Abstract

The effect of light soaking on photoconductivity and DC CPM absorption spectra in hydrogenated silicon films with mixed amorphous‐nanocrystalline structure studied. A series of biphase silicon films were deposited using very high frequency plasma‐enhanced chemical vapor deposition (VHF‐PECVD) technique with hydrogen dilution ratios of silane from 10 to 40. The rate of photoconductivity decrease with light soaking time was increasingly suppressed as crystalline volume fraction in the film increased. For silicon films with low crystalline volume fraction, light soaking produced an increase in CPM absorption in the “defect” region of the spectrum at photon energies below 1.4 eV. For silicon films with high crystalline volume fraction, there was no substantial difference between CPM absorption spectra measured before and after light soaking. However, for silicon films with intermediate crystalline grain volume fraction, CPM absorption measurements revealed a dramatic increase in CPM absorption in the energy region (1.2 – 1.7) eV after light soaking. The results obtained indicate a possibility of light‐induced increase in the contribution of crystalline phase to the photoconductivity of silicon films with mixed amorphous‐nanocrystalline structure (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)