Effects of annealing temperature on characteristics of amorphous nickel carbon thin film alloys deposited on n-type silicon substrates by reactive sputtering

The amorphous nickel carbon (a-NiC) thin film alloys were prepared on n-type silicon (n-Si) wafers by reactive sputtering system, which was modified from the radio frequency-plasma enhanced chemical vapor deposition (rf-PECVD) by adding a sputtering target on the top electrode. 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 nickel target surface to dope nickel in a-C film by sputtering. These a-NiC thin film alloys were annealed at the temperatures of 373, 473, 573, 623, 673, and 773 K, and the effects of annealing temperature on the characteristics of a-NiC thin film alloys are investigated. The measured results indicate that the carbon-hydrogen bonds in a-NiC thin film alloys decrease with increasing the annealing temperature from as-deposited to 773 K, but the sp2/(sp2 + sp3) carbon ratio of a-NiC thin film alloys increases from 52 to 82% and the Ni/C ratio of a-NiC thin film alloys also increases from 1.4 to 25.6%. As a result, as the annealing temperature increases from as-deposited to 773 K, the optical band gap of a-NiC thin film alloys decreases from 2 to 0.1 eV and the electrical resistivity of a-NiC thin film alloys decreases from 275 to 3.3 × 10− 3 Ω m. The current density-voltage results show that the a-NiC/n-Si diode exhibits the rectifying behavior, so all the a-NiC thin film alloys annealed at various temperatures are p-type. The a-NiC/n-Si diode has the lowest series resistance of 14.5 Ω and the best ideality factor of 1.4 at the annealing temperature of 673 K.