In situ characterization of microcrystalline silicon by time resolved microwave conductivity

Time resolved microwave conductivity (TRMC) provides the product of the number of free carriers, generated by a laser pulse, by their mobility. A TRMC set-up is implemented in situ together with ultraviolet (UV) visible spectroscopic ellipsometry to analyze and optimize the growth of microcrystalline silicon (μc-Si) by conventional radio frequency discharges. The modelling of TRMC experiment is presented, including numerical simulations of microwave reflectivity, and carrier generation and recombination kinetics. Various materials are analyzed. For the material obtained from SiF₄-H₂ mixtures, the recombination lifetime varies with the power -0.5 of the carrier density, and the best effective mobility is μ_eff = 25(±5) cm² V^-1s^-1. The set-up allows quantitative comparisons with other materials. For μc-Si films deposited by the integrated distributed electron cyclotron resonance (IDECR) technique, we observe a bimolecular recombination at high laser fluence, followed by a monomolecular one. The effective mobility is μ_eff = 6(±2) cm² V^-1 s^-1.