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.