Physical operation of p4-n photodetector has been studied. Photodiode current in the on and off states are presented. The small-signal conductance and junction capacitance versus light intensity are shown. The conductance decreases with intensity due to an increase of photocurrent. The junction capacitance is insensitive to illumination at low intensity and increases significantly at high intensity due to modulation of photogenerated mobile carriers.
J. S. Yuan,
"Design and modeling of p-i-n photodetectors using MEDICI", Proc. SPIE 2149, Technologies for Optical Fiber Communications, (2 May 1994); doi: 10.1117/12.175277; https://doi.org/10.1117/12.175277