Kim Gwang-Sik, Kim Seung-Hwan, Park June, Han Kyu Hyun, Kim Jiyoung, Yu Hyun-Yong
School of Electrical Engineering , Korea University , Seoul 02841 , Korea.
Department of Nano Semiconductor Engineering , Korea University , Seoul 02841 , Korea.
ACS Nano. 2018 Jun 26;12(6):6292-6300. doi: 10.1021/acsnano.8b03331. Epub 2018 Jun 6.
The difficulty in Schottky barrier height (SBH) control arising from Fermi-level pinning (FLP) at electrical contacts is a bottleneck in designing high-performance nanoscale electronics and optoelectronics based on molybdenum disulfide (MoS). For electrical contacts of multilayered MoS, the Fermi level on the metal side is strongly pinned near the conduction-band edge of MoS, which makes most MoS-channel field-effect transistors (MoS FETs) exhibit n-type transfer characteristics regardless of their source/drain (S/D) contact metals. In this work, SBH engineering is conducted to control the SBH of electrical top contacts of multilayered MoS by introducing a metal-interlayer-semiconductor (MIS) structure which induces the Fermi-level unpinning by a reduction of metal-induced gap states (MIGS). An ultrathin titanium dioxide (TiO) interlayer is inserted between the metal contact and the multilayered MoS to alleviate FLP and tune the SBH at the S/D contacts of multilayered MoS FETs. A significant alleviation of FLP is demonstrated as MIS structures with 1 nm thick TiO interlayers are introduced into the S/D contacts. Consequently, the pinning factor ( S) increases from 0.02 for metal-semiconductor (MS) contacts to 0.24 for MIS contacts, and the controllable SBH range is widened from 37 meV (50-87 meV) to 344 meV (107-451 meV). Furthermore, the Fermi-level unpinning effect is reinforced as the interlayer becomes thicker. This work widens the scope for modifying electrical characteristics of contacts by providing a platform to control the SBH through a simple process as well as understanding of the FLP at the electrical top contacts of multilayered MoS.
在基于二硫化钼（MoS）设计高性能纳米级电子器件和光电器件时，电接触处费米能级钉扎（FLP）导致的肖特基势垒高度（SBH）控制困难是一个瓶颈。对于多层MoS的电接触，金属侧的费米能级强烈钉扎在MoS的导带边缘附近，这使得大多数MoS沟道场效应晶体管（MoS FET）无论其源极/漏极（S/D）接触金属如何，都表现出n型转移特性。在这项工作中，通过引入金属 - 中间层 - 半导体（MIS）结构来进行SBH工程，该结构通过减少金属诱导的能隙态（MIGS）来诱导费米能级去钉扎。在金属接触和多层MoS之间插入超薄二氧化钛（TiO）中间层，以减轻FLP并调节多层MoS FET的S/D接触处的SBH。当将具有1 nm厚TiO中间层的MIS结构引入S/D接触时，FLP得到了显著缓解。因此，钉扎因子（S）从金属 - 半导体（MS）接触的0.02增加到MIS接触的0.24，可控的SBH范围从37 meV（50 - 87 meV）扩大到344 meV（107 - 451 meV）。此外，随着中间层变厚，费米能级去钉扎效应增强。这项工作通过提供一个平台来控制SBH，拓宽了通过简单工艺修改接触电特性的范围，同时也加深了对多层MoS顶部电接触处FLP的理解。
