Tuning Carrier Tunneling in van der Waals Heterostructures for Ultrahigh Detectivity.

Semiconducting transition metal dichalcogenides (TMDs) are promising materials for photodetection over a wide range of visible wavelengths. Photodetection is generally realized via a phototransistor, photoconductor, p-n junction photovoltaic device, and thermoelectric device. The photodetectivity, which is a primary parameter in photodetector design, is often limited by either low photoresponsivity or a high dark current in TMDs materials. Here, we demonstrated a highly sensitive photodetector with a MoS/h-BN/graphene heterostructure, by inserting a h-BN insulating layer between graphene electrode and MoS photoabsorber, the dark-carriers were highly suppressed by the large electron barrier (2.7 eV) at the graphene/h-BN junction while the photocarriers were effectively tunneled through small hole barrier (1.2 eV) at the MoS/h-BN junction. With both high photocurrent/dark current ratio (>10) and high photoresponsivity (180 AW), ultrahigh photodetectivity of 2.6 × 10 Jones was obtained at 7 nm thick h-BN, about 100-1000 times higher than that of previously reported MoS-based devices.