Electrical transport phenomena in nanostructured porous-silicon films

Abstract

The charge transport mechanisms in nanostructured porous silicon (PS) films were studied through current-voltage (I-V) measurements of planar Au/PS/Au structures at 300 K. The films were formed by electrochemical etching of 1-5 Ω-cm p-type Si (100) wafers producing PS layers of 4.48 x 109 Ω-cm. The charge transport is limited both by the space charge limited currents (SCLC) and the carrier trapping-detrapping kinetics in the inherent localized PS energy levels. I-V characteristics evolve according to the trapping-detrapping carrier kinetics in the PS films showing that the electrical current can be controlled by applying external electric fields. An equivalent trap filling limiting voltage (VTFL) was identified that shifts between 1 and 3 volts by the carrier trapping-detrapping kinetics from the PS intrinsic defect states. An energy band diagram for the PS films is schematically depicted including the influence of the intrinsic PS defect states. To give a reasonable explanation of the found behavior the existence of a thin silicon oxide film covering the network-like-silicon-nanocrystallites is required, in agreement with the widely accepted PS structural models.