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 hydr ogenated 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 anne aling, following a stretched exponential time dependence with a lower activ ation energy than that for the metastable changes in electronic properties (Staebler-Wronski effect). The absence of metastable XPS changes ill a-Si s uggests that hydrogen may be actively involved in the X-ray irradiation-ind uced structural changes. Our present results suggest that these structural changes may be an independent metastable phenomenon or a precursor process of metastable defect creation. (C) 2001 Elsevier Science B.V. All rights re served.