Highly Efficient Experimental Approach to Evaluate Metal to 2D Semiconductor Interfaces in Vertical Diodes with Asymmetric Metal Contacts

Abstract

The energy band alignments and associated material properties at the contacts between metal and two-dimensional (2D) semiconducting transition metal dichalcogenide (SCTMD) films determine the important traits in 2D SCTMD-based electronic and optical device applications. In this work, we realize 2D vertical diodes with asymmetric metal–SCTMD contact areas where currents are dominated by the contact-limited charge flows in the transport regimes of Fowler–Nordheim tunneling and Schottky emission. With straightforward current–voltage characteristics, we can accurately evaluate the interface parameters such as Schottky barrier heights and the vertical effective masses of tunneling charges. In particular, the differing contact areas and resultant current rectifications allow us to address specific Schottky barrier locations with respect to the conduction and valence band edges of 2D semiconducting WSe2, WS2, MoSe2, and MoS2, thereby determining whether p-type holes or n-type electrons become the majority charge carriers in the SCTMD devices. We demonstrate that our experimental and analytical approaches can be utilized as a simple but powerful material metrology to qualitatively and quantitatively evaluate various metal–SCTMD contacts.

Enhanced Organic Thin-Film Transistor Stability by Preventing MoO3 Diffusion with Metal/MoO3/Organic Multilayered Interface Source-Drain Contact

“…Therefore, Δ E is the LUMO offset of MoO 3 and the OBL materials. There are research data showing that the relation of τ to Δ E obeys the Fowler–Nordheim (FN) tunneling theory. , To confirm the FN tunneling mechanism existing in the MIC device, we fabricated a single-electron diode device with Ag/MoO 3 /NPB/CuPc multilayered interfaces. Its I–V curve was measured, and the related ln­( I / V 2 ) versus 1/ V was plotted in Figure S17, where I is the current of source-drain electrodes of the single-electron device and V is the applied voltage.…”

In Situ Active Switching of Bipolar Current Rectification in 2D Semiconductor Vertical Diodes

“…Considering the work function of clean Au as 4.8–5.1 eV, the work function difference between Au and WSe 2 will induce a p-doping in the WSe 2 layers close to the Au electrode, forming a Schottky contact at the Au/WSe 2 interface. On the other side, the EGaIn electrode has a lower work function of 4.3 eV, which is similar to Ti and may induce n-doping in the WSe 2 layers at the interface . However, the native GaO x layer on the surface of EGaIn should not be overlooked here, especially at the small contact.…”

“…For WSe 2 , it is well known that WSe 2 can function as an ambipolar semiconductor, , in which both p-doping and n-doping regions could be induced at the WSe 2 /electrode interface depending on the work function of the metal electrodes. However, for other TMDC materials, e.g., WS 2 , the large amounts of sulfur vacancies may introduce mid-gap states, leading to a strong Fermi level pinning effect close to the conduction band of WS 2 . Even with high work function metals, such as Pt or Au, the metal-induced doping in WS 2 is usually n-type.…”

“…However, the lateral TMDC diodes have a limited channel cross section due to the nanometer-scale thickness of TMDC flakes and inevitable surface absorbates or defects due to the large-area TMDC surface exposed to the environment, which hinders the performance of lateral TMDC diodes. Alternatively, vertical TMDC diodes show great advantages with the elevated channel cross section, nanometer-scale channel length, and less exposed TMDC surface. − By optimizing the electrode materials and the size of the device, TMDC vertical diodes with high current density, low turn-on voltage, and good current rectifications have been reported . High-frequency vertical TMDC diodes with a cutoff frequency of 27 GHz were also demonstrated using several tens of nanometers thick TMDC flakes to reduce the contact resistance and capacitance .…”

Bias-Modified Schottky Barrier Height-Dependent Graphene/ReSe2 van der Waals Heterostructures for Excellent Photodetector and NO2 Gas Sensing Applications

“…Interestingly, in contrast to graphene (a zero bandgap material) [ 19 ], TMDs have finite bandgap values normally between 0.2 to 3 eV [ 20 ] depending upon the choice of material and its layer thickness and were found to be a potential substitute for traditional narrow bandgap materials for many electronic and optoelectronic applications. Moreover, their properties are strongly influenced by the choice of metal contacts (either ohmic or Schottky), energy band alignment, and types of TMDs [ 21 ]. Additionally, their electro-optical and gas sensor characteristics can also be modified by the electrostatic backgate voltage as well as channel region doping [ 22 , 23 ].…”