Mechanical, electrical and optical properties of a-C : H : N films deposited by plasma CVD technique

Amorphous hydrogenated carbon films with different nitrogen content (a-C:H: N) were deposited (thickness 2.65-3.01 mu m) by plasma-activated chemical v apour deposition of acetylene + nitrogen (0-62 vol%) onto glass/Si substrat es at a deposition temperature of similar to 523 K and a negative bias volt age similar to 500 V. The fundamental optical absorption edge was studied b y optical transmittance measurements. With increasing nitrogen content (0-2 0 at%) in the films the band gap and Urbach tail width decreased. Thick fil ms deposited without nitrogen had high compressive stress (similar to 3 GPa ). Introduction of nitrogen in the precursor gas was effective in reducing the stress to less than 1 GPa with improved adhesion of the film on the sub strate. The stresses in the films were determined by a non-destructive opti cal technique (from the optical absorption band tail) so that the substrate effect on the stress measurement prevalent in the indentation technique co uld be eliminated. Raman, photoluminescence and FTIR spectra were analysed to ascertain the quality of the films. Studies on the temperature dependenc e of the electrical conductivity of the films indicated variable range hopp ing conduction to be predominant at low temperature. (C) 1999 Elsevier Scie nce Ltd. All rights reserved.