Origin of optically induced electron-spin resonance in hydrogenated amorphous silicon

${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ hyperfine structure in an optically induced electron-spin-resonance spectrum has been detected in hydrogenated amorphous silicon using a pulsed technique. The optically induced ESR signal is accompanied by an increase in the subbandgap optical absorption. These observations suggest that the optically induced ESR signals originate from a localized state similar to the singly occupied dangling-bond state observed in dark, which is phenomenologically similar to the defect properties in chalcogenide glasses.