Atomically thin telluride multiheterostructures: toward spatial modulation of bandgaps

Lateral multiheterostructures with spatially modulated bandgaps have great potential for applications in high-performance electronic, optoelectronic and thermoelectric devices. Multiheterostructures based on transition metal tellurides are especially promising due to their tunable bandgap in a wide range and the rich variety of structural phases. However, the synthesis of telluride-based multiheterostructures remains a challenge due to the low activity of tellurium and the poor thermal stability of tellurium alloys. In this work, we synthesized monolayer WSe_2-2xTe_2x/WSe_2-2yTe_2y (x > y) multiheterostructures in situ using chemical vapor deposition (CVD). Photoluminescence analysis and Raman mapping confirm the spatial modulation of the bandgap in the radial direction. Furthermore, field-effect transistors with the channels parallel (type I) and perpendicular (type II) to the multiheterostructure rings were fabricated. Type I transistors exhibit enhanced ambipolar transport, due to the low energy bridges between the source and drain. Remarkably, the photocurrents in type I transistors are two orders of magnitude higher than those in type II transistors, which can be attributed to the fact that the photovoltaic photocurrents generated at the two heterojunctions are summed together in type I transistors, but they cancel each other in type II transistors. These multiheterostructures will provide a new platform for novel electronic/photonic devices with potential applications in broadband light sensing, highly sensitive imaging and ultrafast optoelectronic integrated circuits.