SPICE Modeling in Verilog-A for Photo-Response in UTC-Photodiodes Targeting Beyond-5G Circuit Design

This article reports the first accurate and physics-based Verilog-A implementation of the fully analytic form of photocurrent in SPICE compact models for uni-traveling carrier (UTC) photodiodes (PDs). To overcome the limitations of single-pole network implementations for modeling frequency dependence of the photo-response, especially at frequencies beyond 100 GHz, we explored different solutions for the complete analytic equation of the dynamic photocurrent. A new implementation has been proposed which requires three additional nodes in the UTC-PD electrical equivalent circuit and offers the best tradeoff between accuracy and computational efficiency. Model validation has been performed against on-wafer measurements from two UTC-PD technologies depicting very good accuracy over the entire frequency range.