RESUMEN
In this study, electrical characteristics of MoTe2 field-effect transistors (FETs) are investigated as a function of channel thickness. The conductivity type in FETs, fabricated from exfoliated MoTe2 crystals, switched from p-type to ambipolar to n-type conduction with increasing MoTe2 channel thickness from 10.6 nm to 56.7 nm. This change in flake-thickness-dependent conducting behavior of MoTe2 FETs can be attributed to modulation of the Schottky barrier height and related bandgap alignment. Change in polarity as a function of channel thickness variation is also used for ammonia (NH3) sensing, which confirms the p- and n-type behavior of MoTe2 devices.
RESUMEN
An automated technique is presented for mechanically exfoliating single-layer and few-layer transition metal dichalcogenides using controlled shear and normal forces imposed by a parallel plate rheometer. A thin sample that is removed from bulk MoS2 or MoTe2 is initially attached to the movable upper fixture of the rheometer using blue dicing tape while the lower base plate also has the same tape to capture and exfoliate samples when the two plates are brought into contact then separated. A step-and-repeat exfoliation process is initiated using a preprogrammed contact force and liftoff speed. It was determined that atomically thin films of these materials could be obtained reproducibly using this technique, achieving single-layer and few-layer thicknesses for engineering novel 2D transistor devices for future electronic technologies. We show that varying the parameters of the rheometer program can improve the mechanical exfoliation process.
RESUMEN
Single-crystalline MoSe2 and MoTe2 platelets were grown by Chemical Vapor Transport (CVT), followed by exfoliation, device fabrication, optical and electrical characterization. We observed that for the field-effect-transistor (FET) channel thickness in range of 5.5 nm to 8.5 nm, MoTe2 shows p-type, whereas MoSe2 with channel thickness range of 1.6 nm to 10.5 nm, shows n-type conductivity behavior. At room temperature, both MoSe2 and MoTe2 FETs have high ON/OFF current ratio and low contact resistance. Controlling charge carrier type and mobility in MoSe2 and MoTe2 layers can pave a way for utilizing these materials for heterojunction nanoelctronic devices with superior performance.
RESUMEN
In this study, electronic properties of field-effect transistors (FETs) fabricated from exfoliated MoTe2 single crystals are investigated as a function of channel thickness. The conductivity type in FETs gradually changes from n-type for thick MoTe2 layers (above ≈ 65 nm) to ambipolar behavior for intermediate MoTe2 thickness (between ≈ 60 and 15 nm) to p- type for thin layers (below ≈ 10 nm). The n-type behavior in quasi-bulk MoTe2 is attributed to doping with chlorine atoms from the TeCl4 transport agent used for the chemical vapor transport (CVT) growth of MoTe2. The change in polarity sign with decreasing channel thickness may be associated with increasing role of surface states in ultra-thin layers, which in turn influence carrier concentration and dynamics in the channel due to modulation of Schottky barrier height and band-bending at the metal/semiconductor interface.
