Locally Phase-Engineered MoTe<sub>2</sub> for Near-Infrared\nPhotodetectors

Transition-metal\ndichalcogenides (TMDs) are ideal systems for two-dimensional\n(2D) optoelectronic applications owing to their strong light-matter\ninteraction and various band gap energies. New techniques to modify\nthe crystallographic phase of TMDs have recently been discovered,\nallowing the creation of lateral heterostructures and the design of\nall-2D circuitry. Thus, far, the potential benefits of phase-engineered\nTMD devices for optoelectronic applications are still largely unexplored.\nThe dominant mechanisms involved in photocurrent generation in these\nsystems remain unclear, hindering further development of new all-2D\noptoelectronic devices. Here, we fabricate locally phase-engineered\nMoTe<sub>2</sub> optoelectronic devices, creating a metal (1T′)\nsemiconductor (2H) lateral junction and unveil the main mechanisms\nat play for photocurrent generation. We find that the photocurrent\noriginates from the 1T′–2H junction, with a maximum\nat the 2H MoTe<sub>2</sub> side of the junction. This observation,\ntogether with the nonlinear IV-curve, indicates that the photovoltaic\neffect plays a major role in the photon-to-charge current conversion\nin these systems. Additionally, the 1T′–2H MoTe<sub>2</sub> heterojunction device exhibits a fast optoelectronic response\nover a wavelength range of 700–1100 nm, with a rise and fall\ntimes of 113 and 110 μs, respectively, 2 orders of magnitude\nfaster when compared to a directly contacted 2H MoTe<sub>2</sub> device.\nThese results show the potential of local phase-engineering for all-2D\noptoelectronic circuitry.