Electronic transport in porous silicon of low porosity made p(+) substrate

To analyze the carriers transport in metal-porous silicon (PS) junctions, w e studied the current-voltage and impedance characteristics of a series of junctions, having a typical porosity of 30% and a layer thickness ranging f rom 1.5 to 30 mu m. PS conductivity as a function of the annealing temperat ure showed two characteristic regions at 150 and 550 degrees C where the co nductivity abruptly increased by several orders of magnitude. These tempera tures coincide with the temperature of dissociation of Si-H-B complexes and of hydrogen effusion. After short time rinsing of high temperature anneale d PS in hydrofluoric acid its resistivity returned to the initial high valu e it had in the as-prepared state. These results imply that hydrogen plays a key role in determining the conduction properties of PS. We argue that th e hydrogen present in PS in high concentration effectively passivates the b oron doping atoms. As a result the space charge region that compensates sur face charges significantly widens and becomes essentially larger than the s ilicon wires which leads to the high resistivity of PS. Current-voltage dep endencies exhibit a region of space charge limited current, which allows fo r the determination of the energy distribution density of states in PS. (C) 2000 Elsevier Science S.A. All rights reserved.