Electrical properties of metal/porous silicon/p-Si structures with thin porous silicon layer

Porous silicon (PS) based metal/PS/p-Si structures with PS layer of differe nt thickness were prepared on moderate- and high-resistivity substrates. Me asurements of current-voltage (I-V) characteristics and impedance at variou s temperatures were used for the investigation of the electrical properties of these structures. Electrical properties of the structures with relative ly thin (I Am) PS layer significantly differ from those of thick structures . The exponential forward bias I-V dependencies for thin structures spread over several orders of magnitude with a low value of quality factor (close to 2) and have activation temperature dependencies with an activation energ y equal to half the c-Si band gap. The reverse current has a square root de pendence on the reverse bias voltage and the activation energy is equal to half the c-Si band gap. Therefore, it was concluded that the reverse and fo rward currents in thin PS-based device structures were determined by the ge neration and recombination of carriers in the depletion region of the c-Si substrate. It was shown that a large area spreading current exists in struc tures made on highly resistive substrates, which appears to be due to a hig hly conductive inverse (n-type) layer formed in the p-Si substrate at the P S/p-Si heterojunction. The spreading effect leads to high reverse currents and high capacitance of the device structures made on highly resistive subs trates. (C) 2001 American Institute of Physics.