MoTe2 Field-effect Transistors Research Articles

Non‐Lithographic Fabrication of All‐2D α‐MoTe2 Dual Gate Transistors

As one of the emerging new transition‐metal dichalcogenides materials, molybdenum ditelluride (α‐MoTe2) is attracting much attention due to its optical and electrical properties. This study fabricates all‐2D MoTe2‐based field effect transistors (FETs) on glass, using thin hexagonal boron nitride and thin graphene in consideration of good dielectric/channel interface and source/drain contacts, respectively. Distinguished from previous works, in this study, all 2D FETs with α‐MoTe2 nanoflakes are dual‐gated for driving higher current. Moreover, for the present 2D dual gate FET fabrications on glass, all thermal annealing and lithography processes are intentionally exempted for fully non‐lithographic method using only van der Waal's forces. The dual‐gate MoTe2 FET displays quite a high hole and electron mobility over ≈20 cm2 V−1 s−1 along with ON/OFF ratio of ≈105 in maximum as an ambipolar FET and also demonstrates high drain current of a few tens‐to‐hundred μA at a low operation voltage. It appears promising enough to drive organic light emitting diode pixels and NOR logic functions on glass.

Exfoliated multilayer MoTe2 field-effect transistors

The properties of multilayer exfoliated MoTe2 field-effect transistors (FETs) on SiO2 were investigated for channel thicknesses from 6 to 44 monolayers (MLs). All transistors showed p-type conductivity at zero back-gate bias. For channel thicknesses of 8 ML or less, the transistors exhibited ambipolar characteristics. ON/OFF current ratio was greatest, 1 × 105, for the transistor with the thinnest channel, 6 ML. Devices showed a clear photoresponse to wavelengths between 510 and 1080 nm at room temperature. Temperature-dependent current-voltage measurements were performed on a FET with 30 layers of MoTe2. When the channel is turned-on and p-type, the temperature dependence is barrier-limited by the Au/Ti/MoTe2 contact with a hole activation energy of 0.13 eV. A long channel transistor model with Schottky barrier contacts is shown to be consistent with the common-source characteristics.

Field-Effect Transistors Based on Few-Layered α-MoTe2

Here we report the properties of field-effect transistors based on a few layers of chemical vapor transport grown α-MoTe2 crystals mechanically exfoliated onto SiO2. We performed field-effect and Hall mobility measurements, as well as Raman scattering and transmission electron microscopy. In contrast to both MoS2 and MoSe2, our MoTe2 field-effect transistors are observed to be hole-doped, displaying on/off ratios surpassing 106 and typical subthreshold swings of ∼140 mV per decade. Both field-effect and Hall mobilities indicate maximum values approaching or surpassing 10 cm2/(V s), which are comparable to figures previously reported for single or bilayered MoS2 and/or for MoSe2 exfoliated onto SiO2 at room temperature and without the use of dielectric engineering. Raman scattering reveals sharp modes in agreement with previous reports, whose frequencies are found to display little or no dependence on the number of layers. Given that MoS2 is electron-doped, the stacking of MoTe2 onto MoS2 could produce ambipolar field-effect transistors and a gap modulation. Although the overall electronic performance of MoTe2 is comparable to those of MoS2 and MoSe2, the heavier element Te leads to a stronger spin–orbit coupling and possibly to concomitantly longer decoherence times for exciton valley and spin indexes.