Spectroscopic properties of nitrogen doped hydrogenated amorphous carbon films grown by radio frequency plasma-enhanced chemical vapor deposition

Nitrogen doped hydrogenated amorphous carbon thin films have been deposited by rf plasma-enhanced chemical vapor deposition using CH4 as the source of carbon and with different nitrogen flow rates (N-2/CH4 gas ratios between 0 and 3), at 300 K. The dependence modifications of the optical and the str uctural properties on nitrogen incorporation were investigated using differ ent spectroscopic techniques, such as, Raman spectroscopy, Fourier transfor m infrared spectroscopy, x-ray photoelectron spectroscopy, ultraviolet-visi ble (UV-VIS) spectroscopy, electron spin resonance (ESR), photoluminescence (PL) and spectroscopic ellipsometry (SE). Raman spectroscopy and IR absorp tion reveal an increase in sp(2)-bonded carbon or a change in sp(2) domain size with increasing nitrogen flow rate. It is found that the configuration of nitrogen atoms incorporated into an amorphous carbon network gradually changes from nitrogen atoms surrounded by three (sigma bonded) to two (pi b onded) neighboring carbons with increasing nitrogen flow rate. Tauc optical gap is reduced from 2.6 to 2.0 eV, and the ESR spin density and the peak-t o-peak linewidth increase sharply with increasing nitrogen flow rate. Excel lent agreement has been found between the measured SE data and modeled spec tra, in which an empirical dielectric function of amorphous materials and a linear void distribution along the thickness have been assumed. The influe nce of nitrogen on the electronic density of states is explained based on t he optical properties measured by UV-VIS and PL including nitrogen lone pai r band. (C) 2001 American Institute of Physics.