  Graphene-based vertical field effect transistors have attracted considerable
attention in the light of realizing high-speed switching devices; however, the
functionality of such devices has been limited by either their small ON-OFF
current ratios or ON current densities. We fabricate a graphene/MoS2/metal
vertical heterostructure by using mechanical exfoliation and dry transfer of
graphene and MoS2 layers. The van der Waals interface between graphene and MoS2
exhibits a Schottky barrier, thus enabling the possibility of well-defined
current rectification. The height of the Schottky barrier can be strongly
modulated by an external gate electric field owing to the small density of
states of graphene. We obtain large current modulation exceeding 10^5
simultaneously with a large current density of ~10^4 A/cm^2 , thereby
demonstrating the superior performance of the exfoliated-graphene/MoS2/metal
vertical field effect transistor
