Influence of electron irradiation on the electronic properties of microcrystalline silicon

Electron irradiation with 1-MeV electrons induces pronounced changes in the optical and electronic properties of microcrystalline silicon, namely an increase in sub-gap absorption as measured by the constant photocurrent method and a deterioration of the photoconductive properties for both the majority and minority carriers as measured by steady-state photoconductivity and the steady-state photocarrier grating technique. We conclude from photocurrent spectroscopy that the increase in the recombination centre density upon irradiation is responsible for the change in the film quality. The photocurrent response in the ultraviolet spectral region indicates a spatially homogeneous density of these recombination centres induced by the electron irradiation while in the as-deposited state the spatially inhomogeneous but overall lower defect density increases towards the film/air interface. Conduction by energy-loss hopping explains the insensitivity of the photoconductivity to the electron-induced increase in the gap-state density at temperatures lesser than 10 K.