Separation of planar and edge contributions to total capacitance for accurate doping concentration determination in square silicon photodiodes

Accurately determining the doping concentrations of silicon photodiodes (PDs) is crucial for optimizing their performance in various applications. This study presents a methodology for separating the planar and edge contributions to the total capacitance of square silicon PDs with guard rings. Through capacitance-voltage measurements, we distinguished planar capacitance, which reflects the bulk properties of the silicon PD, from edge capacitance, influenced by device geometry and fringing fields. We demonstrated that the fabricated PDs with guard rings surrounding the active area could be effectively modeled using a coxial-like structure to estimate edge capacitance. Doping concentrations, depletion widths, and resistivities were determined through linear fitting of the inverse square of the measured capacitance per unit area as a function of the reverse bias voltage. All parameters obtained from the full depletion voltage V_d , determined by the intersection of the linear fits for V < V_d and V > V_d , demonstrated agreement within 1σ. Our results underscore the importance of accounting for edge effects to accurately determine doping concentrations from 1/C ² vs. V plots.