EFFECT OF GAS PRESSURE ON THE BORON-DOPED HYDROGENATED AMORPHOUS CARBON THIN FILMS GROWN BY RADIO FREQUENCY PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION

Boron-doped hydrogenated amorphous carbon (a-C:B:H) thin films have been deposited by radio frequency plasma-enhanced chemical vapor deposition (r.f. PECVD) with a frequency of 13.56 MHz at room temperature using pure methane as a precursor of carbon source mixed with hydrogen (H2) as a carrier gas. The films were prepared by varying the r.f. power, different gas flow rates of CH4, and partial pressure of mixed gas (CH4/H2) using boron as a solid target. The thickness, structural bonding, and optical properties of the as-deposited films were studied by Alpha-step surface profiler, Raman spectroscopy (Raman), Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and UV–visible spectroscopy. It was found that changing the deposition pressure in addition of using solid boron target in the r.f. PECVD process has a profound effect on the properties of the deposited films as evidenced from their Raman scattering and optical results. The grown a-C:B:H films were found to be smooth and their thicknesses were in the range of 200 to 400 nm for 1 h of deposition time. Films deposited at lower pressure appear brownish in color, whereas those deposited at higher pressure appear pale yellowish. The as-deposited film was found to be dominated by trigonal (sp2) rather than tetrahedral (sp3), which might be due to the formation of small crystallites. The optical band gap is found to be reduced from 2.60 to 1.62 eV as the partial pressure of CH4/H2 gas is reduced.