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

Abstract

Amorphous carbon nitride (a-CN x ) 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-CN x . 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-CN x 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.

Non-uniform Excitation States in Photoinduced Deformation of Amorphous Carbon Nitride Films

“…If a pattern arises as a result of inhomogeneous secondary electron emission, it indicates that electrons excited by visible light irradiation are localized on the film surface. In fact, the a-CN x films with photomechanical response show little photoconductivity 22 . This experimental fact reinforces the above assumption, which means that the photocarriers generated by visible light are localized in a specific area and behave to change in a structure of the amorphous network.…”

“…Thus, the photothermal effects in the photomechanical response of a-CN x films would be quite weak. Moreover, the photoinduced deformation has been observed in an a-CN x film with high resistivity and low photoconductivity 22 . From these results, we assume that the origin of photoinduced deformation is the same as that of photoconductivity.…”