Light-Induced Degradation in a-Si:H and it's 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 (∼10 μs) precursors of SWE defect creation is presented. Problems with existing SWE models and understanding of defect capture properties are formulated.