Waveguide-integrated mid-IR photodetector and all-optical modulator based on interlayer excitons absorption in a...

Novel 2D van der Waals semiconductors facilitate the formation of heterostructures and thus support bandgap engineering for atomically thin modern photonic applications. When these heterostructures form a type II band structure, interlayer excitons (ILEs) are formed as a result of the ultrafast charge transfer between the layers. Here, we present for the first time a waveguide-coupled, mid-IR photodetector and modulator based on the ILE absorption. The device consists of a heterostructure of a single layer of tungsten disulfide (WS₂) and a few layers of hafnium disulfide (HfS₂) integrated to a silicon waveguide on a sapphire substrate. We measure broadband mid-IR photodetection (3.8-5.5 µm) with responsivity in the order of tens of µA/W and with no significant effect on the waveguide's transmission. Additionally, we demonstrate waveguide-integrated, mid-IR, all-optical modulation by controlling the ILE population with the interband transition of the individual layers of the heterostructure.