Bilayer transition metal chalcogenides (TMDs) have gradually attracted a great deal of attention due to the higher density of states and carrier mobility than monolayer TMDs. Controlling the uniformity of the layer number is very crucial because it will intensively influence the physical properties. However, it is difficult to synthesize equal-bilayer (EB) TMDs with two identical layers via a normal layer-by-layer strategy. Most reported bilayer TMDs are not uniform and such unequal bilayers would introduce a sizable Schottky barrier, resulting in the low carrier mobility. Here, a nucleation-etching strategy is proposed to grow EB-MoSe₂ by chemical vapor deposition (CVD), which breaks the limitations of normal layer-by-layer strategy. The second layer is preferentially formed beneath the first layer rather than above, and a different etching phenomenon is also observed, which occurs more preferentially at the overlapping grain boundary sites on the top layer. The obtained EB-MoSe₂ flakes are 3R-stack with high crystal quality. Furthermore, the contact between EB-MoSe₂ and metal electrodes is greatly improved, thereby EB-MoSe₂ transistors exhibit an order of magnitude higher carrier mobility (104 cm² V^–1 s^–1) than that of UEB-MoSe₂ transistors (12 cm² V^–1 s^–1). This value is also at a relatively high level compared with reported results. Our work offers a feasible strategy for the synthesis of EB-TMDs with high carrier mobility, which is meaningful for developing high-performance 2D optoelectronic devices.

中文翻译：

---

通过成核刻蚀策略生长的等双层 MoSe2，具有高载流子迁移率


双层过渡金属硫属化物 （TMD） 由于比单层 TMD 具有更高的态密度和载流子迁移率，因此逐渐引起了人们的广泛关注。控制层数的均匀性非常重要，因为它会强烈影响物理性质。然而，通过常规的逐层策略合成具有两个相同层的等双层 （EB） TMD 是很困难的。大多数报道的双层 TMD 并不均匀，这种不等的双层会引入相当大的肖特基势垒，导致载流子迁移率低。在这里，提出了一种成核-刻蚀策略，通过化学气相沉积 （CVD） 生长 EB-MoSe₂，这打破了正常逐层策略的限制。第二层优先在第一层下方形成，而不是在第一层上方形成，并且还观察到不同的蚀刻现象，这种现象更优先发生在顶层的重叠晶界位置。获得的 EB-MoSe₂ 薄片是具有高晶体质量的 3R 堆栈。此外，EB-MoSe₂ 与金属电极之间的接触大大改善，因此 EB-MoSe₂ 晶体管的载流子迁移率 （104 cm² V^–1 s^–1） 比 UEB-MoSe₂ 晶体管 （12 cm² V^–1 s^–1） 高一个数量级。与报告的结果相比，该值也处于相对较高的水平。我们的工作为合成具有高载流子迁移率的 EB-TMD 提供了一种可行的策略，这对开发高性能 2D 光电器件具有重要意义。