Continuous-wave and pulsed electron-nuclear double-resonance study of paramagnetic defects in amorphous hydrogenated silicon-carbon alloy

Alloying amorphous hydrogenated silicon with carbon, although increasing the optical band gap, results in a dramatic increase in the number of paramagnetic defects and subsequent deterioration of optoelectronic properties. Electron-nuclear double-resonance and electron spin resonance studies of enriched13 materials provide a picture of how unpaired electrons, silicon atoms, and carbon atoms relate to each other in the alloys. We report the observation of weak hyperfine interactions originating from C13 and Si29 nuclei which are about two bond lengths away from the unpaired electrons. The absence of stronger interactions between unpaired electrons and C13 nuclei indicates that carbon dangling bonds do not exist, even in materials with a high level of paramagnetic defects. We suggest a model involving dangling-bond migration and carbon-double-bond formation to explain these results.