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 MoS₂/h-BN/graphene heterostructure, by inserting a h-BN insulating layer between graphene electrode and MoS₂ 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 MoS₂/h-BN junction. With both high photocurrent/dark current ratio (>10⁵) and high photoresponsivity (180 AW^-1), ultrahigh photodetectivity of 2.6 × 10¹³ Jones was obtained at 7 nm thick h-BN, about 100-1000 times higher than that of previously reported MoS₂-based devices.