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.