Recognizing that monolayer molybdenum disulfide (MoS2) is a direct-bandgap semiconductor due to quantum-mechanical confinement and allows a high absorption coefficient and efficient electron-hole pair generation under photoexcitation, researchers at École Polytechnique Federale de Lausanne (EPFL; Lausanne, Switzerland) have been able to fabricate MoS2-based photodetector devices that are five times more light-sensitive than silicon; photoresponsivity values reach 880 A/W—a 100,000-fold improvement over previous reports for monolayer MoS2 phototransistors.
The photodetectors were fabricated using scotch-tape micromechanical cleavage (similar to some graphene-fabrication techniques) to exfoliate the MoS2 monolayer from molybdenum-doped materials. Monolayer MoS2 flakes were identified based on their optical contrast with respect to the underlying silicon dioxide substrate; 90-nm-thick gold electrodes were then placed on the monolayers and devices were wire-bonded. Because of the direct bandgap, the ultrasensitive MoS2 photodetectors have a photoresponsivity that is 106 better than the first graphene photodetectors, with a 9000-fold higher photoresponsivity observed in monolayer MoS2 compared to multilayer photodetectors. In contrast to silicon photodiodes, MoS2 photodetectors devices consist of a simple n-type channel—much easier to manufacture than a p-n junction and potentially leading to lower production costs. Contact Andras Kis at [email protected].
