Spectral response limitation mechanisms of a shallow junction n+-p photodiode

Modulated monochromatic visible light at various wavelengths was used to generate photocurrent in a silicon n⁺-p diffused diode. A numerical model which includes electric field, heavy doping bandgap reduction, and doping level mobility dependence was used with fitting techniques to determine the carrier lifetime in the n⁺-region at each wavelength. From these measurements it was concluded that the physical mechanisms involved in limiting the spectral response of the n⁺-p photodiode at short wavelengths (0.42 µm) is due to heavy recombination of photogenerated carriers in the n⁺-region. The latter is caused by the heavy doping which results in a fraction of a nanosecond minority carrier lifetime and a retarding or reduced electric field in the n⁺-region. Surface recombination velocity has little influence on this loss mechanism.