CAS Key Laboratory of Nanosystem and Hierarchical Fabrication, National Center for Nanoscience and Technology, Beijing, 100190, China.
Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, No. A35, QingHua East Road, Haidian District, Beijing, 100083, China.
Adv Mater. 2019 Jan;31(1):e1805317. doi: 10.1002/adma.201805317. Epub 2018 Oct 29.
A long-standing puzzle about van der Waals semiconductors (vdWS) is regarding the origin(s) of the conduction behavior they exhibit. Of particular interest are those with ambipolar conduction, which may provide an alternative choice for practical applications when considering the difficulties of doping the ultrathin bodies of vdWS. Here, the conduction behavior of ambipolar vdWS is analytically and theoretically studied. Using numerical simulation, it is shown that ambipolar vdWS can be fully captured by a Schottky-barrier FET model. Based on this, it is found that the widely observed conduction polarity transition while changing the body thickness mainly comes from the tuning of band alignment at the metal/vdWS interfaces. This transition can be suppressed/inversed by introducing an inert hBN layer between the vdWS and the substrate. Through first-principles calculations, it is demonstrated that metal/vdWS/substrate interactions play a crucial role in tuning the Schottky-barrier heights, which finally determines the conduction behavior that ambipolar vdWS exhibit.
范德华半导体（vdWS）的一个长期存在的难题是关于它们表现出的传导行为的起源。特别有趣的是那些具有双极性传导的半导体，当考虑到掺杂 vdWS 的超薄体时，这可能为实际应用提供了另一种选择。在这里，我们对双极性 vdWS 的传导行为进行了分析和理论研究。通过数值模拟，我们表明双极性 vdWS 可以完全被肖特基势垒 FET 模型所捕获。基于这一点，我们发现，在改变体厚度时观察到的广泛的传导极性转变主要来自于金属/vdWS 界面处能带排列的调整。通过在 vdWS 和衬底之间引入惰性 hBN 层，可以抑制/反转这种转变。通过第一性原理计算，证明了金属/vdWS/衬底相互作用在调整肖特基势垒高度方面起着至关重要的作用，最终决定了双极性 vdWS 表现出的传导行为。
