Photo-induced electrical instability in hydrogenated amorphous silicon based thin-film transistors and the effect of its phase transition

• We investigate the origin of photo-induced electrical instability in hydrogenated amorphous silicon thin-film transistors.
• Photo-induced electrical instability was enhanced compared to electrical instability alone.
• Such results can be explained by extended charge trapping and/or defect-states creation.
• We prove that a transition from an amorphous to a protocrystalline phase improve photo-induced electrical stability.

We investigate the origin of photo-induced electrical instability in hydrogenated amorphous silicon based thin-film transistors (a-Si:H TFTs). Photo instability alone was accompanied by a positive shift in the threshold voltage (VTH) caused by photo irradiation, and even larger positive or negative shift further exacerbated the instability caused by photo-induced electrical bias stress. Such phenomena can occur as a result of extended charge trapping and/or the creation of defect-states at the semiconductor/dielectric interface or in the gate dielectric. The mechanism for such is difficult to describe through chemical interactions of electron-donating and -withdrawing molecules that exhibit a shift in VTH in only one direction. We also prove that a transition from an amorphous to a protocrystalline phase improves the photo-induced electrical stability. Such results originate from a reduction in the density of the localized states in protocrystalline-Si:H films relative to that of a-Si:H. We believe that this study provides significant information on the device physics of optoelectronics, which commonly exhibit photo-induced instability and charge transport, as a result of prolonged exposure to photo irradiation.

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