Non-Local Model for the Spatial Distribution of Impact Ionization Events in Avalanche Photodiodes

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Avalanche photodiodes (APDs) are widely deployed in high-data-rate optical-fiber communication and lidar systems that operate at the wavelengths of 1.3 µm. Among the APD structures, the separate absorption, charge and multiplication (SACM) InP-InGaAs APDs have been the preferred structure for two reasons. First, they have high sensitivity, which results from their internal carrier multiplication, namely the avalanche of impact ionizations that result from each photogenerated carrier. Second, they are highly cost effective compared to receivers that employ optical pre-amplification. However, due to the stochastic nature of the impact-ionization process, the multiplication gain comes at the expense of extra noise. This multiplication noise is characterized by a quantity termed “the excess noise factor,” which accounts for the gain uncertainty.