Silane versus silicon tetrafluoride in the growth of microcrystalline silicon films by standard radio frequency glow discharge

Properties of microcrystalline silicon (μc-Si) films produced by standard radio frequency glow discharge from SiH4 or SiF4 precursors were studied. Spectroscopic ellipsometry (SE), Raman spectroscopy and time resolved microwave conductivity (TRMC) were used for their characterisation. Although modelling of SE spectra shows that μc-Si films with crystalline fractions up to 100% can be deposited from both types of precursors, we have found that SiF4 allows obtaining films with improved electronic properties. A detailed analysis of the SE data reveals that such improvement relates to the larger grain size for films deposited from SiF4 in comparison with the ones deposited from SiH4. Interestingly, the deposition rate, the fraction of large grains, and the mobility of carriers for the films grown from SiF4 display close dependencies on the product of pressure and inter-electrode distance. These results are discussed with respect to the contribution of the plasma-synthesised nanocrystals to deposition.