Electrical contacts to two-dimensional semiconductors

Abstract

Semiconducting electronic devices utilize fine control over the flow of charge carriers, which are injected into the semi conducting material through electrical contacts. The quality of the electrical contacts -quantified through contact resistance -is as important to the proper functioning of the entire device as the semiconductor (SC) itself. Since the early 1990s, researchers have explored a wide variety of electronic devices based on nanostruc tures with different dimensionalities, ranging from one dimensional (1D 20 and silicene 21 are also attracting growing interest. One of the most common electronic devices, in both the research and industrial environments, is the fieldeffect transistor (FET). Low contact resistance in 2D SCbased devices is critical for achiev ing high 'on' current, large photoresponse 22 and highfrequency operation 23 . However, the major issue for 2D SC FET transistors is the existence of a large contact resistance at the interface between the 2D SC and any bulk (or 3D) metal, which drastically restrains the drain current [24][25][26] . Contacting 2D SCs presents a certain number of experimental and conceptual challenges. The theoretical concepts that underlie our understanding of conventional metal-SC contacts break down in the limit where the SC thickness is smaller than the The performance of electronic and optoelectronic devices based on two-dimensional layered crystals, including graphene, semiconductors of the transition metal dichalcogenide family such as molybdenum disulphide (MoS 2 ) and tungsten diselenide (WSe 2 ), as well as other emerging two-dimensional semiconductors such as atomically thin black phosphorus, is significantly affected by the electrical contacts that connect these materials with external circuitry. Here, we present a comprehensive treatment of the physics of such interfaces at the contact region and discuss recent progress towards realizing optimal contacts for two-dimensional materials. We also discuss the requirements that must be fulfilled to realize efficient spin injection in transition metal dichalcogenides. depletion and transfer lengths. In the 2D limit, the properties of the interface -the chemical interaction between the metal and the SC -govern everything. Substitutional doping, a common strat egy adopted to decrease the contact resistance in bulk SCs, is not applicable here because it would modify both the 2D material and its properties. In addition, the pristine surface (that is, no dangling bonds) of a 2D material makes it difficult to form strong interface bonds with a metal, thereby increasing contact resistance.The quantum limit to the contact resistance (R C min ) is determined by the number of conducting modes within the SC channel 27,28 , which is connected to the 2D charge carrier density (n 2D ), yielding R C min = h/(2e 2 k F ) = 0.026/√n 2D ≈ 30 Ω μm at n 2D = 10 13 cm -2 (ref. 29) -a value three orders of magnitude below the typical contact resist ance to monolayer MoS 2 . Here, h is Planck's constant, k F is the Fermi wavevector a...

MoS2-graphene in-plane contact for high interfacial thermal conduction

“…As a semiconductor with a direct bandgap (1.8 eV), monolayer MoS 2 is promising in electronic and photonic device applications, including transistors, light-emitters, photovoltaic and photodetectors. 3 With successful growth of MoS 2 on insulating substrates, 4 and significant improvement in its mobility at both low temperature and room temperature, 5−8 it is expected that high-performance fieldeffect transistors based on monolayer MoS 2 will be realized in the near future. In MoS 2 -based integrated devices, naturally, their thermal management will become vitally important.…”

Schottky-Barrier-Free Contacts with Two-Dimensional Semiconductors by Surface-Engineered MXenes

“…transition metal dichalcogenides, black phosphorus) have attracted great interest, their development is significantly hindered by the large Schottky barrier (SB) at the metal-semiconductor junction (MSJ). [14][15][16] Very recently, the use of Ti 2 CT x as electrodes for 2D MoS 2 and WSe 2 field effect transistors have been experimentally demonstrated, yet with significant SBs 17 . Here we predict that SB-free contacts can be achieved by using MXenes with proper surface terminations, which form van der Waals (vdW) junctions 16,18,19 with 2D semiconductors.…”

Role of Charge Traps in the Performance of Atomically Thin Transistors

“…The presence of defects in photodetectors can be beneficial since it has been shown to immobilize charges at the channel which improves the gain in photodetectors [14] and produces nonvolatile memory mechanisms. [15] On the other hand, large hysteresis caused, for example, by charge traps [2] and significant Schottky barriers [16] at the metal-semiconductor interface are still a major design challenge for the realization of novel device architectures. They have been shown to cause degradation in the performance of transistors [17] and generate high levels of flicker noise.…”