The behavior of reverse-biased silicon optical sensors based on non-ideal metal-leaky insulator-silicon (MLIS) capacitors was studied. A highly conductive tin-doped indium oxide film was used as a transparent metallic gate deposited on a leaky insulator containing many through pores. The tin-doped indium oxide, by penetrating in these pores, forms microscopic Schottky diodes on the n-silicon surface. The accumulation of the photo-generated holes under pores-free regions of the insulator surrounding these small-size Schottky diodes gives rise to the experimentally obtained photocurrent gain and self-sustained current oscillations, with a period that depends on the irradiation intensity. The modulation of the Schottky barrier height along the perimeter of the diodes by the holes accumulated under the insulator surrounding these diodes is suggested to explain the behavior of these MLIS structures. The validity of this model was verified by observing a similar behavior in optical sensors with a thermally grown silicon dioxide layer on the silicon surface. In such a case, microscopic Schottky diodes were formed by the penetration of the gate material in small-size "windows" specially etched in the silicon dioxide. © 2006 Elsevier B.V. All rights reserved.
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