Photo-field effect in amorphous silicon thin-film transistors

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Abstract
Amorphous silicon thin-film transistors show a marked photosensitivity, with the illumination producing an increase in the off-current and a negative shift of the threshold voltage. Here we present the results of a complete theory of this photo-field effect, which includes the steady state flux of electrons and holes perpendicular to the source-drain current path. We show that illumination always produces a change in the band bending and a consequent redistribution of the space charge. The theory gives an excellent agreement with the experimental results using a simple model for the density of states in the amorphous silicon.