Contact Engineering of Vertically Grown ReS₂ with Schottky Barrier Modulation

Abstract

Forming metal contact with low contact resistance is essential for the development of electronics based on layered van der Waals materials. ReS2 is a semiconducting transition metal dichalcogenide (TMD) with an MX2 structure similar to that of MoS2. While most TMDs grow parallel to the substrate when synthesized using chemical vapor deposition (CVD), ReS2 tends to orient itself vertically during growth. Such a feature drastically increases the surface area and exposes chemically active edges, making ReS2 an attractive layered material for energy and sensor applications. However, the contact resistances of vertically grown materials are known to be relatively high, compared to those of common 2H-phase TMDs, such as MoS2. Most reported methods for lowering the contact resistance have been focused on exfoliated 2H-phase materials with only a few devices tested, and few works on distorted T-phase materials exist. Moreover, nearly all reported studies have been conducted on only a few devices with mechanically exfoliated fl Most reported methods for lowering the contact resistance have been 2 contacts was modulated by conformally coating a thin tunneling interlayer between the metal and the dendritic ReS2 film. Over a hundred devices were tested, and contact resistances were extracted for large-scale statistical analysis. Importantly, we compared various known materials and techniques for lowering contact resistance and found an optimized method. Finally, the reductions in barrier height were directly correlated with exponential reductions in contact resistance and increases in drive-current by almost 2 orders of magnitude.

High-specific-power flexible transition metal dichalcogenide solar cells

“…Forming a high built-in potential p–n heterojunction (e.g., WSe 2 /MoS 2 ) or homojunction, possibly by metal-oxide-based p-type (MoO x ) and n-type (AlO x ) doping, is another way to achieve a high V OC 23 – 25 , 80 , 82 , 83 . One can also improve the V OC by adopting carrier-selective (MIS) contacts which both de-pin the Fermi level and enable a selective collection of only one type of charge carrier on each side of the solar cell 28 – 31 , 84 , 85 .…”

“…The PCE of TMD solar cells has typically not exceeded 2% 19 – 25 , mostly due to strong Fermi-level pinning at the metal contact–TMD interface 26 and the inapplicability of traditional doping schemes such as diffusion or ion implantation, which can damage TMDs 27 . Reducing or eliminating Fermi-level pinning by adopting a gentle metal transfer method 22 , 26 , introducing an ultrathin interlayer at the metal–TMD interface 28 – 31 , or forming a van der Waals (vdW) heterojunction such as graphene-TMD 32 – 34 can significantly improve the performance of TMD devices. In addition, forming a p–n homojunction by employing TMD-compatible doping methods such as surface charge transfer and fixed charge doping via metal oxides 23 – 25 , plasma doping 35 , or electrostatic doping 36 has been shown to enhance the photovoltaic performance.…”

Photocatalytic Applications of ReS2-Based Heterostructures

“…The two-step method means that the growth of heterostructures is carried out in two separated steps. These methods can realize the high-quality and large-area preparation of single-crystal ReS 2 , which has been widely used in micro-nano electronic devices and photoelectric detection fields [ 22 , 23 , 76 ]. A substantial amount of work has reported the CVD preparation and growth mechanism of ReS 2 heterostructure; readers can refer to the related papers [ 72 , 73 , 74 , 75 , 77 , 78 ] and reviews [ 79 ].…”

Hybrid System Combining Two-Dimensional Materials and Ferroelectrics and Its Application in Photodetection

“…Other methods have therefore been explored. Interlayers between the electrodes and MoS 2 have been introduced, for instance, the ultrathin oxide layer, − graphene, − h -BN, , scandium thin layer, and organic materials, to lower the Schottky barrier. Graphene turns out to be a good candidate for the interlayer of metal/MoS 2 contact because its Fermi level could be effectively tuned by the gate bias, and graphene could form a low-resistance contact with MoS 2 . , Nevertheless graphene is not always suitable as an interlayer for other metal/2D materials contact; for example, the graphene/WSe 2 still forms a Schottky junction due to the large Fermi level difference between graphene and WSe 2 . , Another effective method to optimize the metal contact is to change the top contact (Figure a) to the edge contact (Figure b), which is believed to reduce the contact resistance between metals and 2D materials thanks to an intrinsic higher in-plane conductivity of 2D materials.…”