Fig. 1: Device structure, characteristic curve, and band diagram of DS diode.

a Optical image of graphene/MoS₂/graphite heterojunction diode. Grey, red, and black dashed lines indicate graphite, monolayer MoS₂, and graphene, respectively. We used graphene as a source and graphite as a drain. The top-gate(TG) and control-gate(CG) were placed for gate modulation of the MoS₂ channel and graphene/MoS₂ overlapped region, respectively. Scale bar, 5 um. b Schematic image of graphene/MoS₂/graphite heterojunction diode. c Characteristic drain current(I_D)-bias voltage(V_bias) curve in our device, which exhibits ideality factor(η) = 0.78 in 1 decade of current and an average η < 1 in more than four decades of current, i.e., η_{ave_4dec} < 1. The rectifying ratio of our device is larger than 10⁸. d Band diagram of DS Schottky diode, which explains the working principle of cold electron injection from graphene. E_Dirac, DOS, E_FS, and E_FD indicate Energy at the Dirac point, the density of states, Fermi level at the source side, and Fermi level at the drain side, respectively. Blue dashed line and green arrows indicate MoS₂ energy window level and expression of rapid increment of current flow.