MOS Capacitor-Driven Silicon Modulators: A Mini Review and Comparative Analysis of Modulation Efficiency and Optical Loss

Metal-oxide-semiconductor (MOS) capacitor-driven silicon modulators have demonstrated exceeding performance in driving voltage, energy efficiency, and bandwidth through heterogeneous integration with other active materials, including III-V compound semiconductors, transparent conductive oxides (TCOs), and graphene. However, a proper quantitative comparison is lacking among various device structures due to the difference in material properties and device designs. In this article, we first briefly reviewed state-of-the-art MOS capacitor-driven silicon modulators. Following that, we modeled the modulation efficiency and optical loss of two most representative device structures by incorporating the optical properties such as plasma dispersion, band-filling, and bandgap shrinkage effects for several heterogeneously integrated materials. The comparative analysis based on simulated results shows that Ge, III-Vs, and TCOs all offer larger index modulation than Si, whereas graphene has the largest index modulation. At the end of this article, we discussed the strategy of heterogeneous integration based on device design and scalable fabrication.