Two-Dimensional Material Photodetectors: High Responsivities and Short Response Times of Graphene/Multilayer MoS2 Heterostructures

Wafer-scale and 1-, 3-, and 6-layer MoS₂ films are prepared through the sulfurization of amorphous MoS₂ on sapphire substrates. After transferring a 1-layer of graphene to the MoS₂ films, photodetectors with MoS₂ light absorption and graphene carrier transport layers are fabricated. Compared with the low responsivity values of the standalone MoS₂ device, a 10⁶ responsivity enhancement is observed for the devices with MoS₂ absorption and one-layer graphene carrier transport layers. The phenomenon is attributed to the ultrashort transit time of carriers in the graphene layer and the relatively long carrier lifetime in the MoS₂ layer, which will result in a large photoconductive gain for the graphene/MoS₂ photodetector. Through repeating 3-layer MoS₂ transferring, a device with a 6-layer MoS₂ absorption layer and a 1-layer graphene carrier transport layer can be fabricated. The excess electron storage in the multilayer MoS₂ will help to achieve the charge neutrality in the light absorption layer, and, therefore, the response times of the device would reduce from >50 ms (1-layer MoS₂) to below 10 ms (6-layer MoS₂). The high detectivity of up to 2 × 10¹⁰ Jones of the device has demonstrated the potential of such 2D material heterostructures for photodetector applications at room temperature with high photoconductive gain compatible with avalanche photodetectors.