Straddling Tunneling FETs and Broadband Photodetectors Based on HfS₂/SnS₂ van der Waals Heterostructure

Past studies have shown that vdWHs possess considerable potential for photodetector applications. However, the current performance of 2D material photodetectors falls short of practical demands due to pronounced interfacial recombination, insufficient photoconductive gain, and inefficient photocarrier collection. Straddling (type I) 2D vdWH notably diminishes interfacial trapping, amplifies the photoconductive gain, and facilitates anisotropic photocarrier collection. Tunnel FET (TFET), fabricated from these type I 2D materials, provides enhanced electrostatic control and the capability for substantially higher on-current densities and on/off ratios. However, gaining an understanding of the intricate tunneling mechanisms within type I heterostructures continues to present a significant challenge. In this study, we demonstrate gate-tunable type I tunnel heterostructures utilizing a HfS₂/SnS₂ vdWHs. By employing a single electrostatic gating mechanism with hexagonal boron nitride (h-BN) as the dielectric layer, a variety of electrical transport behaviors, such as forward rectification, Esaki tunneling, and backward rectification, are realized within the same heterostructure at low gate voltage levels of ±3 V. The heterostructure demonstrates distinct room-temperature negative differential resistance (NDR) characteristics, evident at a low bias voltage of ±0.4 V. In darkness, direct tunneling (DT) is the dominant transport mechanism. However, under illumination, the heterostructure exhibits a shift to the Fowler-Nordheim tunneling (FNT) behavior. The type I heterostructures achieved a photoresponsivity (R) of 43 A W^-1 under 455 nm illumination. Furthermore, the device shows an exceptional detectivity (D*) of 4.3 × 10¹¹ Jones and broadband detection capabilities, covering the spectra from ultraviolet to visible light. Our work broadens the range of capabilities for 2D semiconductor devices, highlighting a compelling potential for their utilization in future optoelectronic systems.