†Department of Materials Science and Engineering, ‡Department of Chemistry and Biochemistry, and §California Nanosystems Institute, University of California, Los Angeles, California 90095, United States.
Nano Lett. 2015 May 13;15(5):3030-4. doi: 10.1021/nl504957p. Epub 2015 Apr 22.
Two-dimensional layered semiconductors such as molybdenum disulfide (MoS2) have attracted tremendous interest as a new class of electronic materials. However, there are considerable challenges in making reliable contacts to these atomically thin materials. Here we present a new strategy by using graphene as the back electrodes to achieve ohmic contact to MoS2. With a finite density of states, the Fermi level of graphene can be readily tuned by a gate potential to enable a nearly perfect band alignment with MoS2. We demonstrate for the first time a transparent contact to MoS2 with zero contact barrier and linear output behavior at cryogenic temperatures (down to 1.9 K) for both monolayer and multilayer MoS2. Benefiting from the barrier-free transparent contacts, we show that a metal-insulator transition can be observed in a two-terminal MoS2 device, a phenomenon that could be easily masked by Schottky barriers found in conventional metal-contacted MoS2 devices. With further passivation by boron nitride (BN) encapsulation, we demonstrate a record-high extrinsic (two-terminal) field effect mobility up to 1300 cm(2)/(V s) in MoS2 at low temperature.
二维层状半导体，如二硫化钼 (MoS2)，作为一类新型的电子材料引起了极大的关注。然而，在这些原子级薄的材料上实现可靠的接触仍然存在相当大的挑战。在这里，我们提出了一种新策略，使用石墨烯作为背电极来实现与 MoS2 的欧姆接触。由于石墨烯具有有限的态密度，其费米能级可以通过栅极电势来轻松调节，从而实现与 MoS2 的近乎完美的能带对齐。我们首次证明了在低温下（低至 1.9 K），对于单层和多层 MoS2，石墨烯可实现与 MoS2 的零接触势垒和线性输出特性的透明接触。得益于无势垒的透明接触，我们表明可以在 MoS2 的两端器件中观察到金属-绝缘体转变，这种现象在传统的金属接触 MoS2 器件中由肖特基势垒很容易被掩盖。通过进一步用氮化硼 (BN) 封装进行钝化，我们在低温下实现了高达 1300 cm²/（V s）的 MoS2 的创纪录的高外（两端）场效应迁移率。
