Semimetal-Monolayer Transition Metal Dichalcogenides Photodetectors for Wafer-Scale Ultraviolet Photonics

Atomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS₂, are promising candidates for nanoscale photonics because they demonstrate strong-light matter interactions due to the planar exciton effect and because of their stability in air. However, Fermi level pinning due to metal-induced gap (MIGS) states at the metals-monolayer MoS₂ interface limits the application of optoelectronic devices based on conventional metals because of the relatively high contact resistance of the Schottky contacts that lead to poor current-delivery capability. On the other hand, a semimetal-TMD-semimetal device can overcome this limitation, where the MIGS are sufficiently suppressed and can result in ohmic contacts. Here we demonstrate the optoelectronic performance of a bismuth-monolayer (1L) MoS₂-bismuth device with ohmic electrical contacts and extraordinary optoelectronic properties. To address the wafer-scale production, we grew full coverage 1L MoS₂ by using the solid-source chemical vapor deposition method. We measured high photoresponsivity of 300 A/W in the UV regime at 77 K, which translates into an external quantum efficiency (EQE) ~ 1000 or 10⁵%. By measuring time-resolved photocurrent, we have found that the 90% rise time of our devices at 77 K is 0.1 ms, which suggests that the current devices can operate at the speed of ~ 10 kHz. The combination of large-array device fabrication, high sensitivity, and high-speed response offers great potential for applications in photonics that includes integrated optoelectronic circuits, light sensing, and pixel arrays for high-resolution cameras, biomedical imaging, covert communication, and fire monitoring.