Transport properties and photosensitivity of metal/porous-silicon/c-Si structures

The current-voltage characteristics, photosensitivity, and impedance of p-t ype Al/porous-silicon/c-Si structures with 0.2 to 6-mu m-thick porous layer s of 80% porosity are studied. It is shown that at reverse and small forwar d bias voltages the current is determined by the potential barrier of the c -Si substrate at the isotypic porous-silicon/c-Si heterojunction. The photo sensitivity is determined by the absorption of light in the c-Si substrate. The potential barrier of the metal/porous-silicon contact does not influen ce the photosensitivity or the current-voltage characteristics of the struc tures. The experimental plots of the dependence of the impedance on applied forward bias, thickness of porous silicon layer, and frequency agree well with the theoretical dependences, if an equivalent circuit including two RC circuits connected in series and comprised of the resistance and geometric capacitance of the porous silicon layer and the resistance and capacitance of the potential barrier of the c-Si substrate is used. (C) 1999 American Institute of Physics. [S1063-7826(99)01202-8].