Abstract
Two-dimensional (2D) materials such as Indium Selenide (InSe) is promising for next-generation optoelectronics due to its high carrier mobility and narrow direct band gap (1.26 eV). However, such devices suffer from low responsivity due to low absorption of atomically thin structure. Combining 2D materials with plasmonic nanostructure is an alternative solution for increasing light-matter interaction. Conventionally, researchers utilized metal for plasmonic nanostructure which unfortunately exhibit low quality resonances due to the inherent Ohmic losses. On the other hand, bulk transition metal dichalcogenides possess high refractive index (n > 4) from visible to near-infrared (NIR) region, which make them suitable for making sub-wavelength optical resonators. Herein, we report a MoS2 plasmonic grating enhanced Indium Selenide (InSe) photodetector in near infrared (NIR) with inherent low loss compared to metallic grating. Such MoS2 grating can not only form a n-n heterojunctions with InSe, but also act as a resonator to excite surface plasmon resonance (SPR) resulting in remarkably enhanced light absorption and photoresponsivity in InSe. In this work, by integrating InSe with anisotropic MoS2 grating, we achieved a multi-band resonance in NIR region that are sensitive to either TE or TM polarized light due to different resonance mode. The responsivity of our device shows a 310-fold enhancement compared to pristine device at the resonance wavelength of 870 nm and the maximum detectivity reach 1.02 x 10 <sup>14</sup> Jones, which is the highest value reported for InSe device applied in NIR. This study provides a novel approach for designing high-performance InSe-based polarization-sensitive multi-band photodetectors.