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Owing to its atomically thin thickness, layer-dependent tunable band gap, flexibility, and CMOS compatibility, MoS$_2$ is a promising candidate for photodetection. However, mono-layer MoS2-based photodetectors typically show poor optoelectronic performances, mainly limited by their low optical absorption. In this work, we hybridized CVD-grown monolayer MoS$_2$ with a gold nanodisk (AuND) array to demonstrate a superior visible photodetector through a synergetic effect. It is evident from our experimental results that there is a strong light-matter interaction between AuNDs and monolayer MoS$_2$, which results in better photodetection due to a surface trap state passivation with a longer charge carrier lifetime compared to pristine MoS$_2$. In particular, the AuND/MoS$_2$ system demonstrated a photoresponsivity of $8.7 \times 10^{4}$ A/W, specific detectivity of $6.9 \times 10^{13}$ Jones, and gain $1.7 \times 10^{5}$ at $31.84 \mu W/cm^{2}$ illumination power density of 632 nm wavelength with an applied voltage of 4.0 V for an AuND/MoS$_2$-based photodetector. To our knowledge, these optoelectronic responses are one order higher than reported results for CVD MoS$_2$-based photodetector in the literature., Comment: 30 pages, 14 figures

Modern infrared (IR) microscopy, communication, and sensing systems demand control of the spectral characteristics and polarization states of light. Typically, these systems require the cascading of multiple filters, polarization optics and rotating components to manipulate light, inevitably increasing their sizes and complexities. Here, we report two-terminal mid-infrared (mid-IR) emitters with electrically controllable spectral and polarization properties. Our devices are composed of two back-to-back p-n junctions formed by stacking anisotropic light-emitting materials, black phosphorus and black arsenic-phosphorus with MoS2. By controlling the crystallographic orientations and engineering the band profile of heterostructures, the emissions of two junctions exhibit distinct spectral ranges and polarization directions; more importantly, these two electroluminescence (EL) units can be independently activated, depending on the polarity of the applied bias. Furthermore, we show that when operating our emitter under the polarity-switched pulse mode, its EL exhibits the characteristics of broad spectral coverage, encompassing the entire first mid-IR atmospheric window, and electrically tunable spectral shapes. Our results provide the basis for developing groundbreaking technology in the field of light emitters.

Light-emitting diodes (LEDs) based on III-V/II-VI materials have delivered a compelling performance in the mid-infrared (mid-IR) region, which enabled wide-ranging applications, including environmental monitoring, defense and medical diagnostics. Continued efforts are underway to realize on-chip sensors via heterogeneous integration of mid-IR emitters on a silicon photonic chip. But the uptake of such approach is limited by the high costs and interfacial strains, associated with the process of heterogeneous integrations. Here, the black phosphorus (BP)-based van der Waals (vdW) heterostructures are exploited as room temperature LEDs. The demonstrated devices can emit linearly polarized light, and their spectra cover the technologically important mid-IR atmospheric window (3-4 um). Additionally, the BP LEDs exhibit fast modulation speed as well as exceptional stability, and its peak extrinsic quantum efficiency (QE~0.9%) is comparable to the III-V/II-VI mid-IR LEDs. By leveraging the integrability of vdW heterostructures, we further demonstrate a silicon photonic waveguide-integrated BP LED. The reported hybrid platform holds great promise for mid-IR silicon photonics., Comment: 12 pages, 4 figures