Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
Department of Chemical and Petroleum Engineering, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States.
ACS Nano. 2018 Feb 27;12(2):965-975. doi: 10.1021/acsnano.7b07059. Epub 2018 Jan 23.
Atomically thin transition metal dichalcogenides (TMDs) are of interest for next-generation electronics and optoelectronics. Here, we demonstrate device-ready synthetic tungsten diselenide (WSe) via metal-organic chemical vapor deposition and provide key insights into the phenomena that control the properties of large-area, epitaxial TMDs. When epitaxy is achieved, the sapphire surface reconstructs, leading to strong 2D/3D (i.e., TMD/substrate) interactions that impact carrier transport. Furthermore, we demonstrate that substrate step edges are a major source of carrier doping and scattering. Even with 2D/3D coupling, transistors utilizing transfer-free epitaxial WSe/sapphire exhibit ambipolar behavior with excellent on/off ratios (∼10), high current density (1-10 μA·μm), and good field-effect transistor mobility (∼30 cm·V·s) at room temperature. This work establishes that realization of electronic-grade epitaxial TMDs must consider the impact of the TMD precursors, substrate, and the 2D/3D interface as leading factors in electronic performance.
原子级薄的过渡金属二卤化物（TMDs）是下一代电子学和光电子学的研究热点。在这里，我们通过金属有机化学气相沉积（MOCVD）展示了可用于器件的合成二硒化钨（WSe），并深入了解了控制大面积、外延 TMD 性能的现象。当实现外延时，蓝宝石表面会发生重构，导致强烈的二维/三维（即 TMD/衬底）相互作用，从而影响载流子输运。此外，我们证明了衬底台阶边缘是载流子掺杂和散射的主要来源。即使存在二维/三维耦合，利用无转移外延 WSe/蓝宝石的晶体管仍表现出双极性行为，具有优异的开/关比（约 10）、高电流密度（1-10 μA·μm）和良好的场效应晶体管迁移率（约 30 cm·V·s），工作温度在室温下。这项工作表明，实现电子级外延 TMD 必须考虑 TMD 前体、衬底和二维/三维界面的影响，因为它们是电子性能的主要因素。
