Large‐Scale Transparent Molybdenum Disulfide Plasmonic Photodetector Using Split Bull Eye Structure

DOI: 10.1002/adom.201800461 for use in photodetector and phototransistor.[4,5] The band gap of MoS2 varies from 1.2 to 1.8 eV when the thickness is scaled from bulk to single layer, which allows optical detection from ultraviolet to near-infrared wavelength regime. Apart from mechanical exfoliation of MoS2 using scotch tape,[4] various techniques have been reported to synthesize high-quality MoS2 films which include dilute aqueous solution,[6] liquid exfoliation,[7] physical vapor deposition,[8] sputtering,[9] colloidal MoS2 quantum dot heterojunctions,[10] and more recently chemical vapor deposition (CVD).[11–13] Wafer scale epitaxy growth of MoS2 was also reported using CVD,[14] where homogenous large-scale MoS2 films can be grown which is suitable to demonstrate an array of detector and subsequently realize an imager. However, it is very challenging to grow high-quality, uniform, and defect-free MoS2 film via CVD technique. To achieve detector array with superior performance for nextgeneration imaging application, the use of high-quality material was not the only solution. Apart from growth engineering, it is also important to consider different device design to push the performance to the next level. Use of plasmonic nanostructures is deemed promising to increase optical absorption by coupling with the incident light at the wavelength of surface plasmon resonance for enhancing the overall device performance. To date, various plasmonic structures have been explored to enhance the performance of MoS2 photodetector/phototransistor.[15–18] Plasmonic nanostructures were also employed in MoS2-graphene heterostructures.[19] Hybrid 2D/3D MoS2 nanocrystal on Si platform with superior junction characteristics were reported by Mukherjee et al.[20] Miao et al. reported few layer MoS2 phototransistor with Au nanostructure array operating at 532 nm wavelength.[21] Recently, Li et al. reported plasmonic photodetector operating in between 300 and 800 nm by using Au @ MoS2 core shell heterostructure which achieved a high responsivity value of 22.3 A W−1.[22] However, full detector characterization including noise and detectivity has yet to be reported, which are critical metrics for the imaging system. Moreover, most reports are employing gold (Au) and silver (Ag) as the two widely used plasmonic metals, which are incompatible materials with the mainstream complementary metal-oxide-semiconductor (CMOS) manufacturing technology. Apart from Au and Ag, aluminum (Al) has been reported as a viable plasmonic metal for its useful range in the visible wavelengths.[23] A high performance photodetector array on transparent substrate is highly sought after for enabling next-generation imaging technology at the visible wavelengths. 2D materials such as molybdenum disulfide (MoS2) are attractive for such application owing to its superior optoelectronic properties and transparency when scaled to atomic thinness. Here, direct growth of MoS2 on centimeter-scale transparent Al2O3 substrate is reported using a high yield and scalable chemical vapor deposition approach. This enables a large area photodetector array to be demonstrated, wherein aluminum split bull eye (SBE) plasmonic structure is integrated to achieve further performance boost due to surface plasmon resonance (SPR) effect. For a wavelength of 405 nm, the plasmonic MoS2 detector achieves an ultralow noise equivalent power of ≈6.2 × 10–14 W Hz−1/2 and a high responsivity of 7.26 A W−1 at a small bias of 1.0 V, which is more than 6× larger than the reference detector due to SPR effect. Finite-difference time-domain simulation confirms a higher concentration of optical field distribution at the center of the SBE structure, which is responsible for the enhancement of photocurrent and sensitivity even at low-light condition.