Voltage-tunable side-illuminated graphene–InP Schottky photodetector with enhanced responsivity through multi-layer graphene integration

We propose and theoretically investigate what we believe to be a novel side-illuminated graphene Schottky photodetector (SIGS-PD) integrated on an InP waveguide platform suitable for the telecommunication wavelength of 1.55 µm. Multiple graphene layers (from monolayer to five layers) are positioned to absorb the transverse magnetic (TM) mode, with an InP substrate forming a Schottky junction to enable electrical connectivity and carrier separation. Through electrostatic gating, the graphene Fermi level is actively tuned to reach an epsilon-near-zero condition, transitioning the optical properties from dielectric to metallic. This supports reconfigurable plasmonic modes confined within the subwavelength graphene layer, interacting strongly with the TM optical mode. We demonstrate that a tri-layer graphene structure provides the optimal balance of parameters, achieving a high responsivity of 1.76 A/W at the epsilon-near-zero point for the wavelength of 1.55 µm due to discontinuity and localization of the perpendicular electric field. Dark current is suppressed to 10^-15<i>A</i> by the rectifying Schottky junction, resulting in excellent specific detectivity of 1.2×10¹³<i>J</i><i>o</i><i>n</i><i>e</i><i>s</i>. The exceptional sensitivity and tunable frequency response make this photodetector particularly suitable for applications requiring high-precision light detection, including environmental sensing, biomedical imaging, and low-light communication systems. The voltage tunability of graphene optical properties provides a pathway to dynamically optimize device performance. Compared to existing graphene-based photodetectors, our proposed structure demonstrates superior responsivity while maintaining an extremely low dark current, establishing a promising route toward high-sensitivity photodetectors for integrated photonic circuits.