Space charge limited conduction and electron paramagnetic resonance studies of as grown and nitrogen incorporated tetrahedral amorphous carbon films deposited by pulsed unfiltered cathodic vacuum arc process

Abstract

This paper reports the space charge limited conduction (SCLC) and electron paramagnetic resonance (EPR) studies of as grown and nitrogen incorporated tetrahedral amorphous carbon (ta-C) films deposited by pulsed unfiltered cathodic vacuum arc process. The effect of varying substrate bias and nitrogen content on the properties of as grown and nitrogen incorporated ta-C films have been studied. The values of density of states ( N( E F)) evaluated from SCLC measurements and spin density ( N s) evaluated from EPR studies of as grown ta-C films deposited at 5 V substrate bias are found to be 1.6×10 19 cm −3 eV −1 and 6.7×10 19 cm −3, respectively, which decrease to 8.7×10 18 cm −3 eV −1 and 4.6×10 19 cm −3, respectively, with the increase of substrate bias up to 80 V and beyond 80 V substrate bias these values are found to increase. A small amount of nitrogen incorporation up to 3.6 at.% nitrogen content in nitrogen incorporated ta-C films reduces the values of N( E F) and N s to 1.4×10 19 cm −3 eV −1 and 4.3×10 19 cm −3, respectively. Beyond 3.6 at.% nitrogen content, the values of N( E F) and N s are found to increase monotonically to 2.6×10 19 cm −3 eV −1 and 1.0×10 20 cm −3, respectively, in nitrogen incorporated ta-C films with further increase of nitrogen content up to 15.6 at.%. The local minimum in the values of N( E F) and N s in as grown ta-C films deposited at 80 V substrate bias arises due to the ability of sp 2 sites to pair up. Nitrogen incorporation up to 3.6 at.% in nitrogen incorporated ta-C films seems to compensate the p-type nature and beyond 3.6 at.% nitrogen content the donor electron increases the values of N( E F) and N s in the films.