Origin of saturated light-induced defect density in hydrogenated amorphous silicon

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Abstract
The saturation of light-induced defect density in hydrogenated amorphous silicon (a-Si:H) has been studied as a function of various material parameters, such as initial defect density Ninit, Urbach energy Eu, hydrogen content cH, hydrogenated void fraction R, and deposition-induced annealable defect density ΔNann. These parameters were varied by depositing samples at various substrate temperatures or by postgrowth anneals of samples grown at low substrate temperatures. It is found that total defect density of saturated light-soaked state Nsat is well correlated with the Ninit, Eu, cH, R, and ΔNann in the as-grown states but no correlations between Nsat and parameters other than the Ninit, Eu, and ΔNann in the annealed states are found. It is also observed that annealing before light soaking reduces the Nsat substantially. In particular, it is found that the value of Nsat from the fully annealed state is much lower than that from the as-grown state with similar Ninit and Eu. A possible parameter that plays a primary role in the saturation of light-induced defects is discussed.