We propose a new silicon photodiode model optimized for high-accuracy measurement usage. The new model differs from previous models in that the contribution to the quantum efficiency from the diode front region is described by an integral transform of the equilibrium minority carrier concentration. This description is accurate as long as the recombination of excess minority carriers in the front region occurs only at the front surface and the diode is operating linearly.
Jon Geist and Henry Baltes, "High accuracy modeling of photodiode quantum efficiency," Appl. Opt. 28, 3929-3939 (1989)