Structural, Optical and Electrical Properties of Chemical Vapour Deposited Nitrogen Doped Diamond Like Carbon Films

Aim: Deposition of undoped and nitrogen doped amorphous diamond like carbon films and investigation of improved electrical, optical, field emission as well as structural properties of the films due to nitrogen doping.

Materials and Methods: Nitrogen doped diamond like carbon (N-DLC) films were deposited on silicon and glass substrates by using direct current plasma enhanced chemical vapour deposition (PECVD) process. Precursor gases used were acetylene and nitrogen. The films were characterized by different techniques such as XRD, FTIR, UV-Vis-NIR spectroscopy. Also electrical conductivities and field emission parameters of the films were measured.

Results and Discussion: XRD spectra showed the amorphous nature of the deposited films. Fourier-transform infrared spectroscopy (FTIR) measurements showed different vibrational modes of tetrahedrally bonded carbon present in the DLC films. With the incorporation of nitrogen into the DLC matrix different CN absorption bands appeared in the FTIR spectra. From FTIR spectra variation of sp3/sp2 ratios in the films with nitrogen concentration in the plasma were measured. The results showed that sp3 fraction decreased with increase in nitrogen concentration. N-DLC films showed higher room temperature conductivity and better field emission properties. Tauc gap of the films was decreased with the increase in nitrogen percentage in the plasma, as with the increase of nitrogen content in the DLC films sp2 carbon content was increased, which is consistent with the FTIR results. Nitrogen doped films showed higher emission currents at lower turn-on fields.

Conclusions: FTIR measurements showed various C–H bonding vibrations and different CN absorption bands present in the spectra of N-DLC films, thus confirmed incorporation of nitrogen into DLC matrix. Highest sp3/(sp2+sp3) ~ 85.65% was achieved in the undoped DLC film. N-DLC films showed two orders of magnitude more room temperature conductivity than undoped ones. The lowest turn-on field achieved was 6.56 volt/mm for current density of 0.5 mA/cm2.