Absence of a Band Gap at the Interface of a Metal and Highly Doped Monolayer MoS₂

Abstract

High quality electrical contact to semiconducting transition metal dichalcogenides (TMDCs) such as MoS is key to unlocking their unique electronic and optoelectronic properties for fundamental research and device applications. Despite extensive experimental and theoretical efforts reliable ohmic contact to doped TMDCs remains elusive and would benefit from a better understanding of the underlying physics of the metal-TMDC interface. Here we present measurements of the atomic-scale energy band diagram of junctions between various metals and heavily doped monolayer MoS using ultrahigh vacuum scanning tunneling microscopy (UHV-STM). Our measurements reveal that the electronic properties of these junctions are dominated by two-dimensional metal-induced gap states (MIGS). These MIGS are characterized by a spatially growing measured gap in the local density of states (L-DOS) of the MoS within 2 nm of the metal-semiconductor interface. Their decay lengths extend from a minimum of ∼0.55 nm near midgap to as long as 2 nm near the band edges and are nearly identical for Au, Pd, and graphite contacts, indicating that it is a universal property of the monolayer semiconductor. Our findings indicate that even in heavily doped semiconductors, the presence of MIGS sets the ultimate limit for electrical contact.

Magnetism in semiconducting molybdenum dichalcogenides

“…(d) The temperature dependence of the magnetic fractions VM and V * of the precession and strongly damped signals, respectively (see text). The total magnetic signal is also shown.tensively in the past to study local electronic properties in TMDs and other 2D materials [24].The techniques of STM and µSR complement each other ideally as we are able to study the magnetic properties of these crystals sensitively with µSR experiments, and correlate these magnetic properties with atomic and electronic structure measured by STM. Experimental details are provided in the Methods Section.Zero-field µSR time spectra for single crystalline (Sample A) and polycrystalline (Sample B) samples of MoTe 2 , recorded for various temperatures in the range between 4 K and 450 K, are shown in Figs.…”

“…tensively in the past to study local electronic properties in TMDs and other 2D materials [24].The techniques of STM and µSR complement each other ideally as we are able to study the magnetic properties of these crystals sensitively with µSR experiments, and correlate these magnetic properties with atomic and electronic structure measured by STM. Experimental details are provided in the Methods Section.…”

“…3g (see also the Supplementary Figure 7), which indicate no trace of ESR signal down to the lowest temperature. Previous transmission electron microscopy (TEM) measurements [24] have also shown that one of the prominent defect types in these materials is a chalcogen antisite, where a molybdenum atom replaces the tellurium atom. We therefore proceed to identify it as such.…”

Versatile Crystal Structures and (Opto)electronic Applications of the 2D Metal Mono‐, Di‐, and Tri‐Chalcogenide Nanosheets

“…Rough doping of conventional semiconductors, such as ion implantation doping, is detrimental to 2D metal chalcogenides due to their few‐atomic‐layer thickness. Some special doping technologies aimed at 2D metal chalcogenides have been investigated . Fang et al achieved low contact resistance by doping the vicinities of electrodes through the chemical adsorption of NO 2 on a WSe 2 surface.…”

“…Fang et al achieved low contact resistance by doping the vicinities of electrodes through the chemical adsorption of NO 2 on a WSe 2 surface. [61c] An ionic liquid is an alternative material for chemically doping 2D metal chalcogenides to improve the contact properties. [61b] No feasible scheme exists for substitutional doping in designated regions due to this doping usually being implemented together with the crystal growth process.…”