Tuning Carrier Tunneling in van der Waals Heterostructures for Ultrahigh Detectivity

Abstract

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.

Design and optimization of tunneling photodetectors based on graphene/Al2O3/silicon heterostructures

“…With the insulator acting as the tunneling layer, e.g. hexagonal boron nitride (h-BN), DT occurs at low voltage and the carriers are dominated by F-N tunneling 13 Jones, which is about 100-1000 times higher than those of previously reported MoS 2 -based devices [21]. All these reports found that the embedded h-BN barrier in vertical stacks can dramatically reduce dark current and increase detectivity for photodetector application.…”

“…We believe that optimization of quality of the 2D materials or insulator thickness may obtain short transit time of photogenerated carriers across the channel, enhancing the photoresponse characteristics eventually. Table 1 shows the photoresponse performance of heterojunction tunneling photodetectors, based on different 2D materials and tunneling mechanisms [20,21,23,[34][35][36][37]. In the reported photovoltaic-type devices, photo-induced electron-hole pairs are separated by the built-in electric field, while the carrier tunneling follows different mechanisms.…”

“…Recently, thin insulating films have been successfully employed as the tunneling layer in 2D-material-based photodetectors [19][20][21]. The introduction of the tunneling layer into vertical devices will not further complicate the structure or fabrication process.…”

“…Comparison of 2D materials-based tunneling photodetectors with different tunneling mechanisms.in the high-voltage regime[21]. Park et al demonstrated a Gr/h-BN/MoTe 2 heterostructure, showing excellent photoelectric performance with a responsivity of 610 A/W and a rise time of 0.33 ms[34].…”

Tunneling devices based on graphene/black phosphorus van der Waals heterostructures

“…The surface passivation of this two-dimensional material can be understood by the fact that there are no overhanging chemical bonds on the surface, so van der Waals interactions allow different materials to be superimposed without lattice mismatches. This makes it possible to construct van der Waals heterogeneous structures based on various two-dimensional materials or two-dimensional materials integrated with photon structures [15].…”