Anomalous relaxation of light-induced states of a-Si:H

For a large variety of B, P doped and undoped films, we observed the non-monotonic kinetics of structural changes at elevated temperatures (above 100 C), indicating the coexistence of two processes described by stretched exponentials. While the faster process has characteristics corresponding to the conventional metastable dangling bond creation, the characteristics of the slow process are shown to be anomalous (the activation energy for defect creation higher than that for the normal process and the parameter beta decreasing with temperature). To describe the anomalous process, we propose a phenomenological model based on a three-level configuration-coordinate diagram with correlated activation energies for the light-induced metastable state creation and annealing. The model accounts for the observed features of the anomalous process. A possible underlying microscopic mechanism of structural changes is discussed.