| Summary: | 博士 === 國立中興大學 === 材料科學與工程學系所 === 106 === Effects of radio-frequency (rf) powers and annealing temperatures on characteristics of nickel-carbon (C-Ni films) thin films prepared by reactive sputtering are investigated. The reactive sputtering is a combination of rf-plasma enhanced chemical vapor deposition and sputtering, which is not hazardous and poisonous. 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. The microstructure, chemical composition, and optical and electrical properties of C-Ni films prepared different rf powers and annealing temperatures are examined. Moreover, the C-Ni film is deposited on n-type silicon (n-Si) to construct the C-Ni/n-Si device, and the current density-voltage (J-V) and capacitance density-voltage (C-V) characteristics of C-Ni/n-Si devices are studied.
When changing rf powers at a fixed film thickness of 100nm, the measured results show that the carbon-hydrogen bonds in C-Ni films decrease with increasing the rf power from 50 to 100 W, but no carbon-hydrogen bonds were found in C-Ni films with the rf power above 150 W. As the rf power increases from 50 to 300 W, the Ni/C ratio in C-Ni films increases from 0.2 to 55.8 % and the sp2/(sp2+sp3) carbon ratio in C-Ni films also increases from 40 to 84%. Additionally, the degree of crystallinity of C-Ni films increases with increasing the rf power from 50 to 300 W, and the structure of C-Ni films changes from amorphous carbons to containing an amount of rhombohedral Ni3C compounds. The Ni/C ratio and degree of graphitization of C-Ni films increase with increasing the rf power from 50 to 300 W, so the optical band gap of C-Ni films decreases from 2 to 0 eV and the electrical resistivity of C-Ni films decreases from 3.6×104 to 8.6×10-5 Ω·m. The current density-voltage behavior displays that the C-Ni/n-Si device has the rectifying characteristic. As the C-Ni film was prepared at the rf power of 150 W, the C-Ni/n-Si device has the best ideality factor of 2.6.
On the other hand, the C-Ni films were prepared by as-deposited and annealed at the temperatures of 373, 473, 573, 623, 673, and 773 K. The measured results indicate that the carbon-hydrogen bonds in C-Ni films decrease with increasing the annealing temperature from as-deposited to 773 K, but the sp2/(sp2+sp3) carbon ratio of C-Ni films increases from 52 to 82% and the Ni/C ratio of C-Ni films 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 C-Ni films decreases from 2 to 0.1 eV and the electrical resistivity of C-Ni films decreases from 275 to 3.3×10-3 Ω·m. The current density-voltage results show that the C-Ni/n-Si diode exhibits the rectifying behavior, so all the C-Ni films annealed at various temperatures are p-type. The C-Ni/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. One can predict that the C-Ni/n-Si device has the potential to be applied in the electronic/optoelectronic fields.
|
|---|
