Wavelength-Tunable and High-Performance Graphene/Semiconductor Photodetectors from Visible to Near Infrared Lights

In this paper, we have demonstrated that with an additional 20 nm Al2O3 dielectric layer inserted in between the graphene and MoS2 layers, high responsivities up to 102 A/W are observed for the 1-layer graphene/20 nm Al2O3/1-layer MoS2 photodetector. With the isolation of the MoS2 to the graphene layers, the results demonstrate that besides the photoexcited electron extraction from the MoS2 layer to the graphene layer, the electric dipole formation in the MoS2 layer and, therefore, the induced conductance change in the graphene layer is the other dominant mechanism responsible for the photoresponses of the device. With the high mobility and limited carrier numbers in the 1-layer graphene, a small conductance change will result in significant current change corresponding to the incident light. High responsivities will be observed for photodetectors with the 1-layer graphene carrier transport layer. By replacing the light absorption layer from 1-layer MoS2 to conventional semiconductors, graphene/semiconductor photodetectors have exhibited even higher responsivities up to 104 (Si), 105 (GaAs), and 104 (InP) A/W and cutoff wavelengths corresponding to the bandgaps of the light absorption layers (1.11 μm for Si, 0.87 μm for GaAs, and 0.93 μm for InP). High detectivity values of 1012–1013 jones are also observed for the three devices. Compared with the device with 1-layer graphene, the enhanced responsivity (2-layer) and the depressed responsivity (3-layer) of graphene/Si photodetectors are observed. The results demonstrated that when the graphene layer number increases from 2 to 3, the characteristics of trilayer graphene would gradually move from 2D materials to bulk semimetals, which will result in a limited Fermi level shift of the graphene channel under light irradiations.