Monolayer transition metal dichalcogenides (TMDs) have attracted considerable attention as atomically thin semiconductors for the ultimate transistor scaling. For practical applications in integrated electronics, large monolayer single crystals are essential for ensuring consistent electronic properties and high device yield. The TMDs available today are generally obtained by mechanical exfoliation or chemical vapor deposition (CVD) growth, but are often of mixed layer thickness, limited single crystal domain size or have very slow growth rate. Scalable and rapid growth of large single crystals of monolayer TMDs requires maximization of lateral growth rate while completely suppressing the vertical growth, which represents a fundamental synthetic challenge and has motivated considerable efforts. Herein we report a modified CVD approach with controllable reverse flow for rapid growth of large domain single crystals of monolayer TMDs. With the use of reverse flow to precisely control the chemical vapor supply in the thermal CVD process, we can effectively prevent undesired nucleation before reaching optimum growth temperature and enable rapid nucleation and growth of monolayer TMD single crystals at a high temperature that is difficult to attain with use of a typical thermal CVD process. We show that monolayer single crystals of 450 μm lateral size can be prepared in 10 s, with the highest lateral growth rate up to 45 μm/s. Electronic characterization shows that the resulting monolayer WSe₂ material exhibits excellent electronic properties with carrier mobility up to 90 cm² V⁻¹ s⁻¹, comparable to that of the best exfoliated monolayers. Our study provides a robust pathway for rapid growth of high-quality TMD single crystals.

中文翻译：

---

单层WS2和WSe2大单晶的超快生长


单层过渡金属二硫属化物（TMD）作为用于最终晶体管尺寸的原子薄半导体引起了相当大的关注。对于集成电子器件的实际应用，大型单层单晶对于确保一致的电子性能和高器件产量至关重要。目前可用的 TMD 通常是通过机械剥离或化学气相沉积 (CVD) 生长获得的，但通常具有混合层厚度、有限的单晶域尺寸或生长速率非常慢。单层TMDs大单晶的可扩展和快速生长需要最大化横向生长速率，同时完全抑制垂直生长，这是一个基本的合成挑战，并激发了相当大的努力。在此，我们报告了一种改进的 CVD 方法，具有可控逆流，用于快速生长单层 TMD 的大域单晶。利用逆流精确控制热CVD工艺中的化学气相供应，可以有效防止在达到最佳生长温度之前发生不需要的成核，实现单层TMD单晶在难以达到的高温下的快速成核和生长使用典型的热CVD工艺。我们证明，可以在10 s内制备出横向尺寸为450 μm的单层单晶，横向生长速率最高可达45 μm/s。电子表征表明，所得单层WSe ₂材料表现出优异的电子性能，载流子迁移率高达90 cm ² V ^-1 s ^-1 ，与最好的剥离单层相当。 我们的研究为高质量 TMD 单晶的快速生长提供了一条可靠的途径。