Structural changes in amorphous silicon studied by X-ray photoemission spectroscopy: a phenomenon independent of the Staebler–Wronski effect?

X-ray irradiation- and annealing-induced structural changes in undoped hydrogenated amorphous silicon (a-Si:H) and pure amorphous silicon (a-Si) have been investigated in detail by X-ray photoemission spectroscopy (XPS). The irradiation-induced shifts of both the Si 2s and Si 2p peaks of a-Si:H are found to be unstable even at room temperature. They can be reversed by annealing, following a stretched exponential time dependence with a lower activation energy than that for the metastable changes in electronic properties (Staebler–Wronski effect). The absence of metastable XPS changes in a-Si suggests that hydrogen may be actively involved in the X-ray irradiation-induced structural changes. Our present results suggest that these structural changes may be an independent metastable phenomenon or a precursor process of metastable defect creation.