Recently, two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDC_s) attract remarkable scientific and technological attention. However, the Schottky barriers, formed at the interface between semiconductors and metal electrodes, strongly limit the performance of devices based on 2D TMDCs semiconductors. By utilizing the scanning photocurrent microscopy technique, we studied the lateral Schottky barriers formed at the interface between the metal electrodes and MoS₂/WSe₂ thin films. Spatially resolved short-circuit photocurrent images clearly show that the Schottky depletion region extends a few microns laterally along the channel in our devices. By applying a gate voltage and/or a drain-source voltage, we can effectively change the magnitude and direction of the built-i...[ Read more ]

Recently, two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDC_s) attract remarkable scientific and technological attention. However, the Schottky barriers, formed at the interface between semiconductors and metal electrodes, strongly limit the performance of devices based on 2D TMDCs semiconductors. By utilizing the scanning photocurrent microscopy technique, we studied the lateral Schottky barriers formed at the interface between the metal electrodes and MoS₂/WSe₂ thin films. Spatially resolved short-circuit photocurrent images clearly show that the Schottky depletion region extends a few microns laterally along the channel in our devices. By applying a gate voltage and/or a drain-source voltage, we can effectively change the magnitude and direction of the built-in electric field in these lateral depletion regions, and in turn the magnitude and polarity of the observed photocurrent with the local illumination of a laser spot. The photocurrent of our devices thus shows a strong dependence on the gate bias, the drain-source bias, as well as the laser incident position. Our work not only directly probes the lateral Schottky depletion region but also reveals the important role of it in mediating the photoresponse of 2D material optoelectronic devices.

WTe₂, a type-II Weyl semimetal in the TMDC family, was found to possess large, positive and non-saturating magnetoresistance (MR), which is also known as XMR effect, expanding the research scope in TMDCs. We have systematically studied the magnetotransport properties in exfoliated WTe₂ thin films. Large, positive MR is observed in our WTe₂ device (~6315 %) and shows no sign of saturation up to 14 T. The angle dependent MR(B) scaling behavior reveals the Fermi surface anisotropy of the WTe₂ thin films. The non-linear Hall effect indicates a nearly perfect electron and hole compensation by two-band model fitting, which is supported by the SdH oscillation analysis. The results of temperature-dependent carrier density show a relative change of electron and hole concentration, implying a temperature-driven Lifshitz transition in WTe₂. Associated with the large MR, the turn-on temperature behavior is observed in B-field dependent R(T) curves and can be interpreted by Kohler’s rule. A quantitative analysis of the temperature and thickness dependent transport results of WTe₂ demonstrates that although the charge compensation is important, the carrier mobilities also play an essential role on the magnitude of MR, as well as preserving the non-saturating behavior.

The NbSe₂/WTe₂ van der Waals heterostructure provides an ideal platform to study the interface effect in all-TMDC based superconductor/normal-metal interfaces. In our NbSe₂/WTe₂ hybrid structures, the R(T) curves show a resistance upturn below the NbSe₂ superconducting transition temperature. Meanwhile, a conductance dip accompanied with a double-peak feature in the dI/dV spectra and a negative magnetoresistance are observed, both of which, together with the resistance upturn, can be suppressed by increasing the measuring current. By analyzing the dI/dV spectra with BKT theory, all these results can be interpreted as the suppression of Andreev reflection at the non-transparent NbSe₂/WTe₂ interface.