Modeling and Optimization of Nonlinearity in PIN-Type Position Sensitive Detectors

Position sensitive detectors (PSDs) play a critical role in precision optical systems, where measurement accuracy is strongly dependent on detector linearity. However, the influence of intrinsic region doping and junction type on PSD nonlinearity remains insufficiently understood. In this study, we theoretically investigate the impact of junction configurations on carrier lateral diffusion behavior in PIN-type PSDs. By comparing p-p and n-p junctions formed on the same high-resistivity p-type silicon substrate, we reveal that nonlinearity arises from the distinct lateral electric fields induced by different junction types. A mathematical model describing carrier generation and diffusion is developed using the Lucovsky equation and solved via Green’s function and eigenfunction methods. The results show that p-p junctions exhibit significantly more nonlinear lateral transport than conventional n-p junctions. Numerical simulations using MATLAB closely match the analytical solutions, validating the theoretical model. These findings highlight the critical role of junction design in controlling PSD nonlinearity and provide a robust theoretical basis for optimizing performance in high-precision optoelectronic applications.