Phase patterning for ohmic homojunction contact in MoTe₂

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 10⁶. 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.