Recombination mechanisms in hydrogenated silicon nanocrystalline thin films

The photoconductivity dependences on temperature and illumination intensity were investigated for thin films of hydrogenated nanocrystalline silicon (nc-Si:H) grown by very-high-frequency, plasma-enhanced chemical vapor deposition. The nanocrystalline phase was achieved by heavy hydrogen dilution of silane (SiH 4 ). We find that the activation energy of the photoconductivity is sensitive to the incident illumination intensity for illumination intensities below 6 mW/cm 2 . The photocurrent follows a power-law dependence on illumination intensity (I ph / F γ ), with γ ranging from 0.36 to 0.83. The illumination dependence of the photocurrent suggests 2 different recombination mechanisms depending on temperature. In the lower temperature regime (300–340 K), recombination appears to be dominated by a linear (monomolecular) process, while at higher temperatures (350–400 K), it is likely dominated by a sublinear (bimolecular) process.