Response to visible light in amorphous carbon nitride films prepared by reactive sputtering

Amorphous carbon nitride (a-CNx) deposited by reactive sputtering shows deformation, photoconductive behavior, and thermal radiation by visible light irradiation. In this study, we investigated these photoresponse behaviors of a-CNx. To obtain films with different bonding structures, the films were deposited at various temperatures from 473 to 873 K. A reduction in N/C ratio led to a decrease in C–N bonding fraction and an increase in graphite component. The optical band gaps decreased with increasing temperature. Under white light illumination, the surface temperature of a-CNx increased with the narrowing of the band gap owing to the conversion of photon energy primarily into thermal energy. On the photoconductivity and deformation, a nonlinear relationship to the band gap energy was observed. In addition, both these photoresponses showed opposite trends in relation to the deposition temperature. The photoinduced deformation was suppressed by increasing the graphite component and decreasing the C–N bonding fraction.