Metal/PS/c-Si photodetectors based on unoxidized and oxidized porous silicon

Unoxidized and oxidized porous silicon (PS) based metal/PS/c-Si photodetect or structures have been prepared by anodization of 10 and 20 000 Omega cm p -type silicon (c-Si) substrates. A quantum efficiency up to 0.7-0.8 in the wavelength range 0.4-0.7 mum, a detectivity up to 6 x 10(11) cm Hz(1/2)/W a nd a response time less than 2 ns were obtained. It is shown that the noise characteristics of the best device structures are determined by a generati on current. We found that in oxidized device structures and structures made from highly resistive substrates a highly conductive inversion (n-type) la yer is formed in the c-Si substrate adjacent to the PS/c-Si heterojunction. The presence of this inversion layer leads to an increase of the active de vice area, capacitance, noise current and response time. (C) 2001 Elsevier Science Ltd. All rights reserved.