On the formation process of the Staebler—Wronski effect in a-Si:H deduced from its wavelength dependence

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Abstract
The wavelength dependence of the Staebler—Wronski effect in hydrogenated amorphous Si is analysed using photothermal deflection spectroscopy. The enhancement of the optical absorption by broad-band and monochromatic illumination is associated with Si dangling bonds. This enhancement disappears with annealing at 160°C. Different photon energy thresholds for the creation of photo-induced defects in undoped, phosphorus-doped and boron-doped samples are found. Different saturation levels of metastable defect densities exist for white and subgap monochromatic light illumination. The results are discussed in the light of existing models for the Staebler—Wronski effect and a possible microscopic mechanism is proposed to explain the observed discrepancies in these models. In the heavily doped samples, our results are consistent with the Stutzmann model concerning the occurrence of two microscopic mechanisms of defect formation: the breaking of weak bonds and the activation of initially neutral doping atoms to compensate the charged dangling bonds.