Bonding configurations and optical band gap for nitrogenated amorphous silicon carbide films prepared by pulsed laser ablation

SiCx Ny thin films have been deposited by ablating a sintered silicon carbide target in a controlled nitrogen atmosphere. The structural and the optical properties of the films were investigated by x-rayphotoelectron spectroscopy (XPS) and spectroscopic ellipsometry. The nitrogen content was found to be dependent on the nitrogen partial pressure and did not exceed 7.5%. XPS measurements of the N 1s,C1s, and Si 2p photoelectron peaks pointed out the nitrogen preferential bonding to silicon atoms with a concurrent decrease of the Si–C and Si–Si bond density. A slight increase of sp3 hybridized carbon bonds has been also observed. The optical band gap E g values, obtained from fitting the ellipsometric data with an appropriate multiple layers model, were found to increase up to 2.4 eV starting from a value of 1.6 eV for a non-nitrogenated sample. This finding was related to progressive substitution of the weaker Si–Si bonds by the stronger Si–C and Si–N ones which, presumably, involves the removal of electronic states lying at the band edges.