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 (SiH4). 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 proportional to F-gamma), with gamma 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.