A photodetector including a photodiode formed in a semiconductor substrate
and a waveguide element formed of a block of a high-index material
extending above the photodiode in a thick layer of a dielectric
superposed to the substrate, the thick layer being at least as a majority
formed of silicon oxide and the block being formed of a polymer of the
general formula R.sub.1R.sub.2R.sub.3SiOSiR.sub.1R.sub.2R.sub.3 where
R.sub.1, R.sub.2, and R.sub.3 are any carbonaceous or metal substituents
and where one of R.sub.1, R.sub.2, or R.sub.3 is a carbonaceous
substituent having at least four carbon atoms and/or at least one oxygen
atom.