RF Equivalent Circuit Model for GeSi Quantum Confined Stark Effect Electro-Absorption Modulators

We present an RF equivalent circuit model for GeSi quantum confined stark effect (QCSE) electro-absorption modulator (EAM) integrated in a 300 mm Si photonics platform. The model incorporates two key components: the first captures the contributions from interconnects and bondpads, while the second represents the electrical and optical characteristics of the modulator. The model is validated by fitting it to measured S11 parameters across various EAM lengths under different bias conditions. The derived circuit parameters are subsequently employed to simulate the electro-optic S21 response, successfully estimating the EAM 3dB bandwidth in a good agreement with the measured small-signal modulation response. Additionally, deeper insights about the physical interpretation of the S11 data are obtained by converting the S11 to the impedance (Z) domain. Our model facilitates the analysis of EAM performance under high-speed operation, identifying the limiting factors for further speed enhancement.