Design of a High-Efficiency Hydrogenated Amorphous Silicon Electro-Absorption Modulator with Embedded Graphene Capacitor

Waveguide-integrated electro-optical modulators play a crucial role in the design of new-generation photonic integrated circuits. The target of this paper is to demonstrate the potential offered by the association of graphene (Gr) and hydrogenated amorphous silicon (a-Si:H) in enhancing silicon photonics technology, enabling, in particular, the fabrication of efficient, wide-bandwidth, highly compact active devices. The design of the proposed electro-optic modulator is based on accurate numerical simulations where Gr is explored as the active material, absorbing (or not) the light propagating along the waveguide core, with its absorption coefficient being tunable through the application of an external electric bias. By strategically embedding two Gr monolayers where the propagating optical field is at its maximum, the performance of the modulator is maximized, resulting in a 39.5 GHz 3 dB bandwidth, corresponding to a 0.34 dB/µm modulation depth. The straightforward feasibility of the proposed structure is bolstered by the use of the Plasma-Enhanced Chemical Vapor Deposition technique, which allows for the deposition of a-Si:H on a silicon-on-insulator platform as a post-processing phase, ensuring potential scalability and practical implementation for advanced photonics.