The implantation of an additional p+ layer into the substrate of a silicon n+-p photodiode is theoretically evaluated as a method for adjusting its spectral response. It is shown that a fairly small p+-p potential barrier so created will greatly reduce the collection of electrons excited by long-wavelength photons in the bulk of the substrate. A suitable doping concentration is estimated at 1017 cm−3 by computer simulation. It is also found that boron-ion implantation in the energy range 300–800 keV will ensure adjustment of the spectral response in the visible range. A manageable analytical model is constructed.