Semiconductor to metal transition in MoTe2
TL;DR: In this paper, electrical resistivity measurements at high temperatures were carried out in a closed vessel, with the sample in equilibrium with its own vapour pressure, and the properties of α and β-MoTe 2 were discussed in terms of a schematic energy level diagram.
About: This article is published in Journal of Solid State Chemistry.The article was published on 1970-08-01. It has received 106 citations till now. The article focuses on the topics: Transition temperature & Vapor pressure.
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TL;DR: Laser-induced phase patterning is used to fabricate an ohmic heterophase homojunction between semiconducting hexagonal and metallic monoclinic molybdenum ditelluride that is stable up to 300°C and increases the carrier mobility of the MoTe2 transistor by a factor of about 50, while retaining a high on/off current ratio of 106.
Abstract: Artificial van der Waals heterostructures with two-dimensional (2D) atomic crystals are promising as an active channel or as a buffer contact layer for next-generation devices. However, genuine 2D heterostructure devices remain limited because of impurity-involved transfer process and metastable and inhomogeneous heterostructure formation. We used laser-induced phase patterning, a polymorph engineering, to fabricate an ohmic heterophase homojunction between semiconducting hexagonal (2H) and metallic monoclinic (1T') molybdenum ditelluride (MoTe2) that is stable up to 300°C and increases the carrier mobility of the MoTe2 transistor by a factor of about 50, while retaining a high on/off current ratio of 10(6). In situ scanning transmission electron microscopy results combined with theoretical calculations reveal that the Te vacancy triggers the local phase transition in MoTe2, achieving a true 2D device with an ohmic contact.
888 citations
TL;DR: The results suggest that mechanical strains reduce the band gap of semiconducting TMDs causing an direct-to-indirect band gap and a semiconductor- to-metal transition, and highlight the importance of tensile and pure shear strains in tuning the electronic properties of T MDs.
Abstract: Semiconducting transition metal dichalcogenides (TMDs) are emerging as the potential alternatives to graphene. As in the case of graphene, the monolayer of TMDs can easily be exfoliated using mechanical or chemical methods, and their properties can also be tuned. At the same time, semiconducting TMDs (MX2; M = Mo, W and X = S, Se, Te) possess an advantage over graphene in that they exhibit a band gap whose magnitude is appropriate for applications in the opto-electronic devices. Using ab initio simulations, we demonstrate that this band gap can be widely tuned by applying mechanical strains. While the electronic properties of graphene remain almost unaffected by tensile strains, we find TMDs to be sensitive to both tensile and shear strains. Moreover, compared to that of graphene, a much smaller amount of strain is required to vary the band gap of TMDs. Our results suggest that mechanical strains reduce the band gap of semiconducting TMDs causing an direct-to-indirect band gap and a semiconductor-to-metal...
796 citations
TL;DR: In this paper, a structural phase transition between the hexagonal and stable monoclinic (distorted octahedral or 1T′) phases in bulk single-crystalline MoTe2 was shown.
Abstract: Monoclinic transition metal dichalcogenides offer the possibility of topological quantum devices, but they are difficult to realize. One route may be through switching from the common hexagonal phase, for which a method is now shown. Layered transition metal dichalcogenides (TMDs) have attracted renewed interest owing to their potential use as two-dimensional components in next-generation devices1,2. Although group 6 TMDs, such as MX2 with M = (Mo, W) and X = (S, Se, Te), can exist in several polymorphs3, most studies have been conducted with the semiconducting hexagonal (2H) phase as other polymorphs often exhibit inhomogeneous formation1,4,5,6. Here, we report a reversible structural phase transition between the hexagonal and stable monoclinic (distorted octahedral or 1T′) phases in bulk single-crystalline MoTe2. Furthermore, an electronic phase transition from semimetallic to semiconducting is shown as 1T′-MoTe2 crystals go from bulk to few-layered. Bulk 1T′-MoTe2 crystals exhibit a maximum carrier mobility of 4,000 cm2 V−1 s−1 and a giant magnetoresistance of 16,000% in a magnetic field of 14 T at 1.8 K. In the few-layered form, 1T′-MoTe2 exhibits a bandgap opening of up to 60 meV, which our density functional theory calculations identify as arising from strong interband spin–orbit coupling. We further clarify that the Peierls distortion is a key mechanism to stabilize the monoclinic structure. This class of semiconducting MoTe2 unlocks the possibility of topological quantum devices based on non-trivial Z2-band-topology quantum spin Hall insulators in monoclinic TMDs (ref. 7).
790 citations
01 Jan 2012
TL;DR: In this article, the authors demonstrate the importance of tensile and pure shear strains in tuning the electronic properties of semiconducting transition metaldichalcogenides (TMDs) by illustrating a substantial impact of the strain on semiconductor-to-metal transition.
Abstract: Semiconducting transitionmetaldichalcogenides (TMDs) are emerging as the potential alternatives to gra- phene. As in the case of gra- phene, the monolayer of TMDs can easily be exfoliated using me- chanical or chemical methods, and their properties can also be tuned. At the same time, semiconducting TMDs(MX2;M=Mo,WandX=S, Se, Te) possess an advantage over grapheneinthattheyexhibitabandgapwhosemagnitudeisappropriateforapplicationsintheopto- electronicdevices.Usingabinitiosimulations,wedemonstratethatthisbandgapcanbewidelytuned by applyingmechanicalstrains.While theelectronic propertiesof grapheneremain almost unaffected by tensile strains, we find TMDs to be sensitive to both tensile and shear strains. Moreover, compared to that of graphene, a much smaller amount of strain is required to vary the band gap of TMDs. Our results suggest that mechanical strains reduce the band gap of semiconducting TMDs causing an direct-to-indirect band gap and a semiconductor-t o-metal transition. These transitions, however, significantly depend on the type of applied strain and the type of chalcogenide atoms. The diffuse nature of heavier chalcogenides require relatively more tensile and less shear strain (when the monolayerisexpandediny-directionandcompressedinx-direction) toattainadirect-to-indirectband gap transition. In addition, our results demonstrate that the homogeneous biaxial tensile strain of around 10% leads to semiconductor-to-metal transition in all semiconducting TMDs, while through pureshearstrainthistransitioncanonlybeachievedbyexpandingandcompressingthemonolayerof MTe2in the y-andx-directions, respectively. Our results highlight the importance of tensile and pure shear strains in tuning the electronic properties of TMDs by illustrating a substantial impact of the strain on going from MS2 to MSe2 to MTe2.
591 citations
TL;DR: In this article, the authors report ambipolar charge transport in α-molybdenum ditelluride (MoTe2 ) flakes, whereby the temperature dependence of the electrical characteristics was systematically analyzed.
Abstract: We report ambipolar charge transport in α-molybdenum ditelluride (MoTe2 ) flakes, whereby the temperature dependence of the electrical characteristics was systematically analyzed. The ambipolarity of the charge transport originated from the formation of Schottky barriers at the metal/MoTe2 contacts. The Schottky barrier heights as well as the current on/off ratio could be modified by modulating the electrostatic fields of the back-gate voltage (Vbg) and drain-source voltage (Vds). Using these ambipolar MoTe2 transistors we fabricated complementary inverters and amplifiers, demonstrating their feasibility for future digital and analog circuit applications.
385 citations
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TL;DR: The transition metal dichalcogenides are about 60 in number as discussed by the authors, and two-thirds of these assume layer structures and can be cleaved down to less than 1000 A and are then transparent in the region of direct band-to-band transitions.
Abstract: The transition metal dichalcogenides are about 60 in number. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to less than 1000 A and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of electrical and structural data available to yield useful working band models that are in accord with a molecular orbital approach. Several special topics have arisen; these include exciton screening, d-band formation, and the metal/insulator transition; also magnetism and superconductivity in such compounds. High pressure work seems to offer the possibility for testing the recent theory of excitonic insulators.
3,313 citations
Journal Article•
TL;DR: In this paper, a short-range interaction is discussed which couples the charge carriers in highly anisotropic layer structures to the nonpolar optical lattice modes, and the relatively low room-temperature mobilities as well as the high values of the exponents $n$ are explained in terms of the proposed interaction.
Abstract: The electrical resistivities and the Hall constants of the compound semiconductors GaSe, Mo${\mathrm{S}}_{2}$, Mo${\mathrm{Se}}_{2}$, and W${\mathrm{Se}}_{2}$, which crystallize in layer structures, have been measured at temperatures ranging from 100 to 700\ifmmode^\circ\else\textdegree\fi{}K. The Hall mobilities derived from these measurements are all of the order of 100 ${\mathrm{cm}}^{2}$/V sec at room temperature, and they exhibit a temperature dependence of the form $\ensuremath{\mu}\ensuremath{\propto}{(\frac{T}{{T}_{0}})}^{\ensuremath{-}n}$, where $n=2.1$ for GaSe, $n=2.6$ for Mo${\mathrm{S}}_{2}$, and $n=2.4$ for Mo${\mathrm{Se}}_{2}$ and W${\mathrm{Se}}_{2}$. A short-range interaction is discussed which couples the charge carriers in highly anisotropic layer structures to the nonpolar optical lattice modes. The relatively low room-temperature mobilities as well as the high values of the exponents $n$ are explained in terms of the proposed interaction.
485 citations
TL;DR: The structures of WTe2 and a high-temperature monoclinic polymorph of MoTe2 have been solved by Patterson methods as mentioned in this paper, where single crystals were grown by vapor transport methods.
Abstract: The structures of WTe2 and a high-temperature monoclinic polymorph of MoTe2 have been solved by Patterson methods Single crystals were grown by vapor transport methods Cell dimensions, as measured on precession photographs, are for WTe2, a=6282/~, b= 3496/~, c= 14"073 A Similarly for MoTe2, a=633 A, b=3469/~, c=1386/~, B=93°55 Intensities were measured for both crystals from zeroand first-level Weissenberg photographs WTe2 and MoTe2 are given the space groups Pnm21 and P21/m, respectively Minimum function maps prepared by a superposition method gave approximate trial structures for both compounds which were refined by least-squares methods to R values of 125 % and 13-9 % for WTe2 and MoTe2 respectively Both compounds are layer structures with double sheets of tellurium atoms bound together by interleaving metal atoms An off-center positioning of metal atoms in the tellurium octahedra buckles the tellurium sheets and allows metal atoms in adjacent octahedra to approach each other Each metal atom, therefore, has eight neighbors, six tellurium atoms and two metal atoms, and a significant amount of metal-metal bonding is introduced
326 citations
01 Jan 1968
241 citations