Transient response of electrically active grain boundaries in polycrystalline semiconductors

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Abstract
In many polycrystalline semiconductors, the current transport is controlled by potential barriers formed at the grain boundaries. We investigate the response of ZnO grain boundaries to high-voltage pulses with risetime of less than 1 μs. The experimental results, in particular the voltage overshoot effect, cannot be explained by the dynamics of electrons (majority carriers) alone. A model which includes holes (generated by hot electrons in the depletion regions) yields an appreciable overshoot when the steady state is close to a current-voltage bistability. In this case, the approach to equilibrium is altered by the delayed response of the barriers to the presence of holes. Further implications of the model are also discussed.

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