High-Speed Electro-Optic Modulator Based on Chemical-Vapor-Deposited Graphene with van der Waals Hybrid Dielectric

Graphene-based optoelectronic devices have shown high bandwidth and easy incorporation in silicon photonics. However, given that graphene is a single-atom-thick material with a large surface-to-volume ratio, the intriguing properties of the graphene optoelectronic devices are very susceptible to surrounding environments, including interfacial states and dangling bonds from dielectrics. This has degenerated the performance of graphene electro-optic modulators that rely on uniform electrical gating. Herein, a facile integration of a Sb₂O₃/Al₂O₃ hybrid dielectric on the chemical-vapor-deposited (CVD) graphene is reported for electro-absorption modulators. The Sb₂O₃ molecular crystal as interfacial layer enables a homogeneous Al₂O₃ dielectric growth and a van der Waals (vdW) interface with graphene, which can significantly reduce the interfacial scattering centers (such as dangling bonds) and thus preserves the electronic properties of graphene, showing an averaged carrier mobility (μ) of 10880 cm² V^-1 s^-1 and residual carrier concentration (n^*) of 1.35 × 10¹¹ cm^-2. In contrast to the device with a single dielectric, the electro-absorption modulator with the vdW interface shows a 1.6 times higher modulation efficiency (0.0054 dB V^-1 µm^-1) and 5.8 times higher bandwidth (≈35 GHz). Moreover, modulation rate is up to 30 Gbit s^-1. Our work provides a promising dielectric option for graphene optoelectronic devices.