Fine-Tuning of Relative Fraction of Amorphous and Crystalline Phases in Hydrogenated Silicon Prepared by PE-CVD Method

In the present study, nc-Si:H thin films have been deposited from rf-PE-CVD method. A set of depositions was achieved by varying deposition pressure from 234 mTorr to 1 Torr, while all other deposition parameters were kept constant. Structural, optical and electrical properties of the films were investigated in detail. Deposition pressure is found to be a crucial parameter in fine-tuning the material properties including relative fraction of amorphous and crystalline phases. Results indicate that film growth rate critically depends on plasma chemistry/gas phase chemistry governed by variation in deposition pressure. Deposition rate increased monotonically with increase in deposition pressure. Structural properties were studied by Raman spectroscopy and low angle XRD and the results shows that films are nanocrystalline over entire range of deposition pressure studied. Hydrogen content in the films was found < 11 at. % and decreases with increase in deposition pressure. Bandgap was found independent of deposition pressure while photoconductivity decreased by one order from 10-4 S/cm. Surface morphology of films was studied by AFM.