Light-induced degradation in a-Si:H and its relation to defect creation

Light-induced degradation of the photoconductivity of hydrogenated amorphous silicon, a-Si:H, called the Staebler-Wronski effect (SWE) is caused by the creation of defects that act as recombination centers. The creation efficiency as well as its kinetics is essentially the same between 4 and 300 K despite drastic changes in the recombination processes. Defects are created with the same spin signature but with greatly different thermal stability and electron capture cross sections. There appears to be a strong link between the latter two properties. The creation-annealing hystereses of free carrier lifetime and defect concentration are explained. The SWE is reduced in high electric fields at 4.2 K suggesting the possible importance of non-radiative geminate recombinations. The validity of accepted rate equations for the SWE excited by cw and laser pulses is questioned. Evidence for long-lived (similar to10 mus) precursors of SWE defect creation is presented. Problems with existing SWE models and understanding of defect capture properties are formulated. (C) 2002 Elsevier Science B.V. All rights reserved.