Semiconducting Behavior, Schottky Barriers and Field Effect Transistors in Ultrathin Rhenium DiSulfide*

We report the fabrication, characterization, and device characteristics of exfoliated dual-gated ReS$_{2}$ Field Effect Transistors (FETs). All devices were created on few-layer crystals isolated using micromechanical exfoliation of source material grown by molecular beam epitaxy. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy found the composition of the source material to be 34{\%} Re and 66{\%} S. A combination of atomic force microscopy, optical microscopy, and photoluminescence (PL) measurements were used to estimate the number of ReS$_{2}$ layers (2-7) in all fabricated devices. Source and drain contacts were created using a combination of electron beam lithography and e-beam evaporation of 10 nm Cr / 40 nm Au. The ReS$_{\mathrm{2}}$ FETs showed n-type behavior with an on-off ratio of 10$^{\mathrm{5}}$ and a maximum field-effect mobility of 16 cm$^{\mathrm{2}}$\textbullet V$^{\mathrm{-1}}$\textbullet s$^{\mathrm{-1}}$ at room temperature. The contact resistance was determined using the transfer length method and was found to be gate bias dependent ranging from 175 k$\Omega $\textbullet $\mu $m to 5 k$\Omega $\textbullet $\mu $m. Additionally, the contact resistance showed an exponential dependence on back-gate voltage, indicating Schottky barriers at the source and drain contacts. Dual-gated FETs were fabricated with an e-beam-evaporated alumina gate dielectric and a Cr/Au top-gate. The dual-gated FETs demonstrated current saturation and voltage gain with a subthreshold swing of 148 mV/decade.