Center for Joining and Electronic Packaging, State Key Laboratory of Material Processing and Die & Mold Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology , Wuhan 430074, P.R. China.
ACS Nano. 2017 Feb 28;11(2):1964-1972. doi: 10.1021/acsnano.6b08109. Epub 2017 Feb 13.
Phase engineering of two-dimensional (2D) transition metal dichalcogenides (TMDs) such as MoTe offers tremendous opportunities in various device applications. However, most of the existing methods so far only address the small-area local phase change or the growth of certain kinds of phases of MoTe film by laser irradiation, mechanical strain, or procursor type. Obtaining facile, tunable, reversible, and continuous-phase transition and evolution between different phases in direct growth of large-area, few-layer MoTe still remains challenging. Here, we develop a facile method to achieve phase control and transition and report a highly tunable, tellurization velocity-dependent metallic-semiconducting-metallic phase evolution in chemical vapor deposition (CVD) growth of large-area, few-layer MoTe. We found four different phase stages, including two different types of coexistence phases of both 2H and 1 T' phases, 100% 2H phase, and 100% 1T' phase, would emerge, relying on the adopted tellurization velocity. Importantly, the tellurization velocity should be extremely controlled to obtain 100% 2H phase MoTe, while 100% 1T' phase requires a fast tellurization velocity. We further found that such metallic-semiconducting-metallic phase evolution took place with a homogeneous spatial distribution and differs from previous reports in which obvious phase separations are usually found during the phase transition. The resulting MoTe shows high quality with room-temperature mobility comparable with mechanically exfoliated materials. The results might impact large-scale phase engineering of TMDs and other 2D materials for Weyl semimetal topological physics and potential 2D semiconductor device applications.
二维（2D）过渡金属二卤族化合物（TMD）的相工程，例如 MoTe，在各种器件应用中提供了巨大的机会。然而，迄今为止，大多数现有的方法仅通过激光辐照、机械应变或前体类型来解决 MoTe 薄膜的小面积局部相变化或某些种类的相生长。在大面积、少层 MoTe 的直接生长中，获得简便、可调、可逆和连续的相转变和不同相之间的演化仍然具有挑战性。在这里，我们开发了一种简便的方法来实现相控制和转变，并报告了在化学气相沉积（CVD）生长大面积、少层 MoTe 中高度可调的、碲化速度依赖的金属-半导体-金属相演化。我们发现，依赖于采用的碲化速度，会出现四个不同的相阶段，包括两种不同类型的共存相 2H 和 1 T' 相、100% 2H 相和 100% 1T' 相。重要的是，应该极其控制碲化速度以获得 100% 2H 相 MoTe，而 100% 1T' 相需要快速的碲化速度。我们进一步发现，这种金属-半导体-金属相演化是在均匀的空间分布中发生的，这与之前的报告不同，在之前的报告中，通常在相转变过程中发现明显的相分离。所得到的 MoTe 具有高质量，室温迁移率可与机械剥离材料相媲美。该结果可能会影响 TMD 和其他二维材料的大规模相工程，用于 Weyl 半金属拓扑物理和潜在的二维半导体器件应用。
