Influence of Sub-Gap Illumination on Light-Induced ESR in Undoped a-Si:H

Light-induced ESR (LESR) in undoped hydrogenated amorphous silicon (a-Si:H) excited simultaneously with band-gap light (1.75 eV) and infrared (IR) light of either photon energy E < 0.99 eV (IR1) or E < 0.7 eV (IR2) was studied. Both the IR1 and IR2 lights decrease all three components (the narrow, broad and neutral dangling bond components) of the 1.75 eV LESR signal, but the IR1 light has a stronger effect than the IR2 light. While the IR2 light decreases the spin density of both the broad component (N b) and the narrow component (N n), which means the N b/N n ratio remains approximately constant and independent of the IR2-light intensity, the IR1 light decreases the broad component more markedly so that the N b/N n ratio decreases with increasing IR1-light intensity. The illumination of a-Si:H films with IR light alone gives an LESR signal only in the case of IR1.