Integration of Refractive Microlenses on BP/MoS₂ Photodiodes for Enhanced Infrared Photodetection

The van der Waals materials have emerged as promising candidates for infrared (IR) photodetectors. Among these, black phosphorus (BP)/ molybdenum disulphide (MoS₂) photodiodes have shown high specific detectivity at room-temperature. The signal-to-noise performance of such detectors can be further improved by employing a microlens to increase the total photon collection without changing the device size, and hence its noise current. In this study, we explore the direct integration of refractive microlenses on BP/MoS₂ photodiodes, designed for operation at a wavelength of λ = 1.55 µm. The device's photoresponse is enhanced by up to 20× after microlens fabrication, enabling a detectivity of 1.83 × 10⁹ cmHz^1/2W^-1 under zero-bias at room-temperature. Infrared imaging is achieved by integrating the device into a single-pixel imaging set-up. This enables a 255 × 192-pixel image to be resolved from the transmission of a binary mask placed in front of a λ = 1.55 µm light source. These results demonstrate that direct integration of refractive microlenses with van der Waals photodiodes provides a simple and scalable route to enhance detectivity at room-temperature, enabling practical near-infrared computational imaging.