Liu Song, Liu Yang, Holtzman Luke, Li Baichang, Holbrook Madisen, Pack Jordan, Taniguchi Takashi, Watanabe Kenji, Dean Cory R, Pasupathy Abhay N, Barmak Katayun, Rhodes Daniel A, Hone James
Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States.
Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, United States.
ACS Nano. 2023 Sep 12;17(17):16587-16596. doi: 10.1021/acsnano.3c02511. Epub 2023 Aug 23.
Two-dimensional transition-metal dichalcogenides (TMDs) have attracted tremendous interest due to the unusual electronic and optoelectronic properties of isolated monolayers and the ability to assemble diverse monolayers into complex heterostructures. To understand the intrinsic properties of TMDs and fully realize their potential in applications and fundamental studies, high-purity materials are required. Here, we describe the synthesis of TMD crystals using a two-step flux growth method that eliminates a major potential source of contamination. Detailed characterization of TMDs grown by this two-step method reveals charged and isovalent defects with densities an order of magnitude lower than those in TMDs grown by a single-step flux technique. For WSe, we show that increasing the Se/W ratio during growth reduces point defect density, with crystals grown at 100:1 ratio achieving charged and isovalent defect densities below 10 and 10 cm, respectively. Initial temperature-dependent electrical transport measurements of monolayer WSe yield room-temperature hole mobility above 840 cm/(V s) and low-temperature disorder-limited mobility above 44,000 cm/(V s). Electrical transport measurements of graphene-WSe heterostructures fabricated from the two-step flux grown WSe also show superior performance: higher graphene mobility, lower charged impurity density, and well-resolved integer quantum Hall states. Finally, we demonstrate that the two-step flux technique can be used to synthesize other TMDs with similar defect densities, including semiconducting 2H-MoSe and 2H-MoTe and semimetallic -WTe and 1T'-MoTe.
二维过渡金属二硫属化物（TMDs）因其孤立单层的异常电子和光电特性以及将多种单层组装成复杂异质结构的能力而引起了极大的关注。为了理解TMDs的本征特性并充分实现其在应用和基础研究中的潜力，需要高纯度材料。在此，我们描述了一种使用两步助熔剂生长法合成TMD晶体的方法，该方法消除了一个主要的潜在污染来源。通过这种两步法生长的TMDs的详细表征揭示了带电和等价缺陷，其密度比通过单步助熔剂技术生长的TMDs低一个数量级。对于WSe₂，我们表明在生长过程中增加Se/W比可降低点缺陷密度，以100:1比例生长的晶体的带电和等价缺陷密度分别低于10¹¹和10¹² cm⁻²。单层WSe₂的初始温度相关电输运测量结果显示，室温空穴迁移率高于840 cm²/(V·s)，低温无序限制迁移率高于44,000 cm²/(V·s)。由两步助熔剂生长的WSe₂制备的石墨烯-WSe₂异质结构的电输运测量也显示出优异的性能：更高的石墨烯迁移率、更低的带电杂质密度以及分辨良好的整数量子霍尔态。最后，我们证明两步助熔剂技术可用于合成具有类似缺陷密度的其他TMDs，包括半导体2H-MoSe₂和2H-MoTe₂以及半金属1T'-WTe₂和1T'-MoTe₂。
