National High Magnetic Field Lab, Florida State University , 1800 East Paul Dirac Drive, Tallahassee, Florida 32310, United States.
Department of Physics and Center for 2-Dimensional and Layered Materials, Pennsylvania State University , University Park, State College, Pennsylvania 16802, United States.
Nano Lett. 2015 Dec 9;15(12):8377-84. doi: 10.1021/acs.nanolett.5b04100. Epub 2015 Nov 30.
In ReS2, a layer-independent direct band gap of 1.5 eV implies a potential for its use in optoelectronic applications. ReS2 crystallizes in the 1T'-structure, which leads to anisotropic physical properties and whose concomitant electronic structure might host a nontrivial topology. Here, we report an overall evaluation of the anisotropic Raman response and the transport properties of few-layered ReS2 field-effect transistors. We find that ReS2 exfoliated on SiO2 behaves as an n-type semiconductor with an intrinsic carrier mobility surpassing μ(i) ∼ 30 cm(2)/(V s) at T = 300 K, which increases up to ∼350 cm(2)/(V s) at 2 K. Semiconducting behavior is observed at low electron densities n, but at high values of n the resistivity decreases by a factor of >7 upon cooling to 2 K and displays a metallic T(2)-dependence. This suggests that the band structure of 1T'-ReS2 is quite susceptible to an electric field applied perpendicularly to the layers. The electric-field induced metallic state observed in transition metal dichalcogenides was recently claimed to result from a percolation type of transition. Instead, through a scaling analysis of the conductivity as a function of T and n, we find that the metallic state of ReS2 results from a second-order metal-to-insulator transition driven by electronic correlations. This gate-induced metallic state offers an alternative to phase engineering for producing ohmic contacts and metallic interconnects in devices based on transition metal dichalcogenides.
在 ReS2 中，1.5eV 的独立层带隙意味着其在光电子应用中的潜在用途。ReS2 结晶为 1T'-结构，导致各向异性的物理性质，其伴随的电子结构可能具有非平凡的拓扑结构。在这里，我们报告了对少层 ReS2 场效应晶体管的各向异性 Raman 响应和输运性质的综合评估。我们发现，在 SiO2 上剥离的 ReS2 表现为 n 型半导体，本征载流子迁移率超过μ(i)∼30cm2/(V s)，在 2K 时增加到∼350cm2/(V s)。在低电子密度 n 下观察到半导体行为，但在高 n 值下，电阻率在冷却到 2K 时下降了>7 倍，并显示出金属 T(2)依赖性。这表明 1T'-ReS2 的能带结构对垂直于层施加的电场非常敏感。最近有人声称，在过渡金属二卤化物中观察到的电场诱导金属态是由渗流型转变引起的。相反，通过对电导率作为 T 和 n 的函数的标度分析，我们发现 ReS2 的金属态是由电子相关驱动的二阶金属-绝缘体转变引起的。这种栅极诱导的金属态为基于过渡金属二卤化物的器件提供了一种产生欧姆接触和金属互连的替代相工程方法。
