OPTICALLY INDUCED METASTABLE DEFECTS IN UNDOPED A-SI-H

A pulsed electron spin resonance (ESR) technique has been applied to undoped hydrogenated amorphous silicon (a-Si:H) to obtain a detailed spectrum of optically induced ESR over a wide dynamic range, and to measure the spin-lattice relaxation curve directly in the time domain. It has been found that the optically induced ESR spectrum involves a Si-29 hyperfine structure which is like that of the dangling-bond state in the dark, and that the spin-lattice relaxation curve in the dark and under optical excitation are quite similar. It has also been found that the optically induced ESR signal accompanies an increase in the sub-bandgap optical absorption. These observations suggest that the optically induced ESR originates from the localized states similar to singly occupied dangling-bond states. The phenomenological similarity of the optically induced ESR in undoped a-Si:H with that in chalcogenide glasses as well as in amorphous arsenic is pointed out and discussed in terms of the network connectivity.