The effect of different radio-frequency powers on characteristics of carbon-titanium nanocomposite thin films prepared by reactive sputtering

The effect of radio-frequency (rf) powers on the characteristics of carbon-titanium nanocomposite thin films (C-Ti films) prepared by reactive sputtering is investigated. The C-Ti films were prepared on n-type silicon (n-Si) wafers by reactive sputtering, which was the combination of rf plasma enhanced chemical vapor deposition (rf-PECVD) and sputtering. Pure methane was used as the precursor gas to form the amorphous carbon (a-C) film by rf-PECVD, and argon was used as the sputtering gas to bombard the titanium target surface to dope titanium in a-C films by sputtering. Seven kinds of C-Ti films were prepared with the rf power being 50, 100, 150, 200, 250, 300, and 350 W, and all the thickness of C-Ti films were fixed at 100 nm at various rf powers. The measured results indicate that the carbon-hydrogen bonds in C-Ti films decrease with increasing the rf power from 50 to 350 W, but the degree of graphitization of C-Ti films increases. The Ti/C ratio of C-Ti films increases from 0.3 to 116% with increasing the rf power from 50 to 350 W, and the sp(2) /(sp(2) + sp(3)) carbon ratio of C-Ti films also increases from 14.7 to 44%. On the other hand, the C-Ti films are amorphous at the rf power from 50 to 250 W, but nano-crystalline titanium carbide grains are encapsulated in a-C matrix at the rf powers of 300 and 350 W. Furthermore, the optical band gap of C-Ti films decreases from 2.6 to 0 eV with increasing the rf power from 50 to 350 W, and the electrical resistivity of C-Ti films decreases from 2.1 x 10(3) to 5 x 10(-6) Omega.m. This implies that the C-Ti film changes from semiconductor to conductor with increasing the rf power from 50 to 350 W. The current density-voltage results show that the C-Ti/n-Si device prepared at various rf powers exhibits the rectifying behavior. The C-Ti/n-Si device prepared at the rf power of 300 W has a best ideality factor of 2.1. The C-Ti/n-Si device has the potential to be applied in the electronic/optoelectronic fields.