Abstract

The volume dark current in a conventional avalanche photodiode arises from random electron-hole pair generations in the depletion volume of the device. This process can be characterized by an average multiplication (gain) 〈M_d〉 and an excess noise factor F_d. Because of the randomness in the locations of the carrier generations, the gain is smaller and the excess noise factor is larger than the usual values associated with injected electrons 〈M_g〉 and F_e). Expressions for 〈M_d〉 and F_d are presented and graphically displayed. Use of these formulas in the SNR gives rise to results that differ from those obtained by assuming that the dark current multiplies in the same manner as injected carriers. The distinction can be important in the case of multiplication-noise-limited operation.