Ultrafast Carrier Dynamics in Undoped Microcrystalline Silicon

We have studied ultrafast dynamics of photoexcited carriers in μc-Si:H by pump and probe laser spectroscopy. We have found that the dynamics of photoexcited carriers in μc-Si:H depend on the crystallinity of the material: in the samples with low crystalline fraction, the dynamics have a fast decay and resemble those in a-Si:H, while in the samples with high crystallinity the dynamics are slower and similar to those in c-Si. We have identified an intensity dependent bimolecular recombination in the samples with lower crystalline fraction (coefficient B = 2×10-10 cm3 s-1 for deposition with silane dilution ratio ≈5% at a fixed power of 6 W), and no bimolecular recombination in the samples with high crystallinity.