Electro-optic modulators (EOMs) are essential components for communications systems, enabling light to be encoded with information and distributed to the world. Data traffic has grown tremendously in recent years which puts strain on current communication links to operate at high bandwidths and require little power. This dissertation discusses the design and optimization of hybrid bonded silicon (nitride) / lithium-niobate [Si(N)/LN] EOMs for high-speed, low-voltage, and high optical power handling operations. The heterogeneous combination of Silicon-on-insulator (SOI) wafers with thin-film lithium niobate (TFLN) offers a platform that takes advantage of the large EO Pockels effect of TFLN, as well as the low-cost, scalable, and well-established SOI foundry technology. By carefully designing the Si(N) waveguide dimensions and introducing periodic slow-wave features in the traveling wave electrodes, broad frequency modulation is demonstrated across operational wavelengths from the telecom to the visible regimes. The results presented here pave way for record-breaking modulator efficiencies and a map for integration with a host of Si photonic components.