Charge Density Depinning in Defective MoTe₂ Transistor by Oxygen Intercalation

Abstract

Molybdenum ditelluride is prone to various defects. Among them, tellurium vacancies lead to the significant reduction of band gap as revealed by density functional theory (DFT) calculations. They are responsible for inducing spatial band structure variation and localized charge puddles in MoTe 2. As a result, undesirable charge density pinning is anticipated in the channel-dominated MoTe 2 field-effect transistors (FETs) even with much improved ohmic contacts, resulting in poor device characteristics, for example, conductivity minimum point (CMP) pinning and weak gate tunability. DFT simulations suggest occupying tellurium vacancies with oxygen can effectively restore MoTe 2 to its intrinsic properties and therefore remove charge density pinning. Experimentally, this can be realized by oxygen intercalation during low-pressure annealing without bringing in additional defects to MoTe 2. The CMP is unpinned in the FETs made of annealed MoTe 2 , which can be tuned by changing the contact metals with varied work functions. Moreover, much improved device characteristics, for example, a high hole current density exceeding 20 μAμm −1 , a record high hole mobility of 77 cm 2 V −1 s −1 , are obtained.

Multilayer MoTe2 Field‐Effect Transistor at High Temperatures

“…Our MoTe 2 samples are exhibiting more p-type behavior at high temperature, therefore, there is more probability of oxidation defects instead of Te vacancies because the chalcogenide vacancies in semiconducting TMDCs are typically reported to induce defect states close to the conduction band edge. [34] Liu et al reported charge traps depth of around 0.24 to 0.018 eV depending on applied V G , [21] and interestingly our measured E a range agrees with their provided numbers. With the increase of temperature, more charge carriers gain sufficient energy to surmount the defect states energy barrier.…”

“…where k B is the Boltzmann constant. [20][21][22] Figure 6c shows the E a as a function of V G by fitting the Arrhenius plot between logarithmic of G and T −1 . The obtained E a values vary from 0.22 to 0.12 eV when V G was swept from 0 to 100 V, which approximately depicts the energy depth of charge traps around the valence band maxima.…”

“…[19] In both the reported studies, the authors attributed the polarity transition to the thermally induced metal-MoTe 2 contact modifications, although the carrier transport in defective devices is governed by channel transport. [20][21][22] This motivates us to systematically investigate the carrier transport in MoTe 2 devices over a wide temperature window with a special focus on channel transport. [17] Here, we designed controllable electro-thermal experiments from room temperature (RT) to high temperatures and employed to the back gated multilayer MoTe 2 field-effect transistors (FETs).…”

Intercalation Strategy in 2D Materials for Electronics and Optoelectronics

“…[ 41 ] Oxygen has been intercalated into MoTe 2 to remove charge density pinning, which improves hole mobility up to 77 cm 2 V –1 s –1 and hole current density over 20 µA µm –1 . [ 42 ] Li intercalation in multilayer WSe 2 field‐effect transistor (FET) reduces both Schottky and electrostatic potential barriers at the vdW interfaces, thereby improving the carrier transport. [ 43 ] These superior performances resulted from intercalation may provide an excellent platform for high performance electronic and optoelectronic devices based on 2D materials.…”

Current‐Induced Complementary Doping to Graphene from Hydrogen Silsesquioxane Passivation Layer

“…The 2D materials, including graphene, transition metal dichalcogenides, and black phosphorous, have been attracting increasing interests during the past decade owing to their attractive properties, such as high carrier mobility, [1][2][3] tunable bandgap, [4] and anisotropic conductivity, [5] leading to possible applications in the fields of electronics [6,7] and optoelectronics. [8] To achieve specific functionalities, such as tuning the electronic properties, [9] contact engineering, [10] forming p-n junctions, doping techniques for 2D materials are necessary. For 2D materials, surface charge transfer has been demonstrated as an efficient doping technique.…”