Inter-Site Fluctuation Mechanics and Generation-Recombination Noise in PIN Photodiodes and Optical Receivers

High-speed optical communication links, quantum key distribution (QKD) receivers, and laser heterodyne radiometers rely heavily on PIN photodiodes to convert optical power into electrical signals. However, ultimate receiver sensitivity, noise equivalent power (NEP), and low-frequency spectral baseline stability are frequently constrained by generation-recombination noise in the depletion region, interfacial trap capture-emission kinetics, and non-stationary bulk leakage currents that standard white shot-noise models fail to capture. In this work, we extend our first-principles inter-site fluctuation mechanics to the electrodynamic transport regime of PIN photodiode junctions. We formulate a stochastic master equation coupling optical generation rates with distributed trap-assisted tunneling and inter-site defect kinetics across the i-region. We derive the exact non-stationary noise spectral density and its convolution with junction electric field distributions, establishing how localized trapping centers manifest as anomalous low-frequency noise in optical receiver baselines. Finally, we outline a MATLAB simulation architecture to validate noise equivalent power floors across operational optical modulation regimes.