Ultraviolet light induced annihilation of silicon dangling bonds in hydrogenated amorphous silicon nitride films

We report results of electron paramagnetic resonance, photothermal deflection spectroscopy, and capacitance-voltage measurements on amorphous hydrogenated silicon nitride (a-SiNx:H) thin films exposed to ultraviolet (UV) illumination. It has been previously shown that exposure to UV light activates silicon dangling-bond defects, i.e., K0 centers, in a-SiNx:H thin films. Here, we demonstrate that the initially UV-activated K0 center can be irreversibly annihilated at long illumination times. Because this effect seems to scale with H content of the measured films, we propose that hydrogen may be passivating the K0 defects during the extended UV exposure. We also show that films subjected to long UV exposures trap charge as efficiently as those having much larger K0 concentrations. A few possibilities to explain this effect are discussed.