Artificial van der Waals heterostructures with two-dimensional (2D) atomic crystals are promising as an active channel or as a buffer contact layer for next-generation devices. However, genuine 2D heterostructure devices remain limited because of impurity-involved transfer process and metastable and inhomogeneous heterostructure formation. We used laser-induced phase patterning, a polymorph engineering, to fabricate an ohmic heterophase homojunction between semiconducting hexagonal (2H) and metallic monoclinic (1T') molybdenum ditelluride (MoTe2) that is stable up to 300°C and increases the carrier mobility of the MoTe2 transistor by a factor of about 50, while retaining a high on/off current ratio of 10(6). In situ scanning transmission electron microscopy results combined with theoretical calculations reveal that the Te vacancy triggers the local phase transition in MoTe2, achieving a true 2D device with an ohmic contact.

Despite several years of research into graphene electronics, sufficient on/off current ratio I(on)/I(off) in graphene transistors with conventional device structures has been impossible to obtain. We report on a three-terminal active device, a graphene variable-barrier "barristor" (GB), in which the key is an atomically sharp interface between graphene and hydrogenated silicon. Large modulation on the device current (on/off ratio of 10(5)) is achieved by adjusting the gate voltage to control the graphene-silicon Schottky barrier. The absence of Fermi-level pinning at the interface allows the barrier's height to be tuned to 0.2 electron volt by adjusting graphene's work function, which results in large shifts of diode threshold voltages. Fabricating GBs on respective 150-mm wafers and combining complementary p- and n-type GBs, we demonstrate inverter and half-adder logic circuits.

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