All-silicon color-sensitive photodetectors in the visible

The particular structure and physico-chemical properties of porous silicon has stimulated the use of this material in many different applications. In the field of optoelectronics, the possibility of fabricating layered structures where each individual layer has different optical properties allows the formation of silicon based optical interference filters. In the present work, porous silicon-based multilayer structures have been used to filter incident light reaching a Si photosensitive wafer, in order to tailor its spectral response. The optical behavior of the porous silicon filters was simulated prior to its fabrication, and optical measurements showed good agreement between the simulated and experimental spectra. Highly doped silicon wafers were used as the active photodetecting layer, since its low resistivity greatly enhances responsitivity, thus obtaining all-silicon filtered photodetecting elements. Photocurrent measurements have shown that the porous silicon filters narrowed the spectral responsitivity of p+ silicon down to typically 150 nm. Accordingly, the sensitivity peak can be tuned along the visible wavelength, from green to near infrared. These devices open the way to the development of easy to fabricate, low cost color photodetectors entirely based on silicon.