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 $^{13}\mathrm{enriched}$ 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 $^{13}\mathrm{C}$ and $^{29}\mathrm{Si}$ nuclei which are about two bond lengths away from the unpaired electrons. The absence of stronger interactions between unpaired electrons and $^{13}\mathrm{C}$ 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.