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Conspectus Two-dimensional (2D) heterostructures have created many novel properties and triggered a variety of promising applications, thus setting off a boom in the modern semiconductor industry. As the first road to step into adequately exploring the properties and real applications, the material preparation process matters a lot. Adhering to the concept of epitaxial growth, chemical vapor deposition (CVD) shows great potential for the preparation of heterostructures for commercialization. At this stage, the growth of 2D heterostructures through CVD methods is still in its infancy in spite of the fact that a great number of 2D heterostructures have been obtained via the CVD process. In order to maximize the excellent properties of 2D heterostructures as well as the compatibility with device engineering, a great deal of effort has been devoted to the CVD growth process of 2D heterostructures with large domain size, high-quality features, and high stability. However, most heterostructures still suffer from the problems of thermally induced degradation, ill-controllable growth directions, and limited material combinations, which will further affect device performance. The main reason is that there is a lack of in-depth understanding of the underlying growth mechanisms, which is of great significance for the development of state-of-the-art optoelectronic devices. In this Account, we first discuss the fundamental mechanisms of the controlled growth of 2D heterostructures to realize in-plane epitaxy or the vertical stack during CVD growth. Two key parameters should be considered during the growth process: growth kinetics and thermodynamics. Then we present the natural heteroepitaxy behaviors between different material systems. Generically, components with similar crystal structures tend to form lateral heterostructures, while for components with different crystal structures, vertical heterostructures are more favorable. Several approaches to the engineering of growth directions and nucleation sites of 2D heterostructures are presented, which provide both theoretical and experimental guidance for the controllable growth of 2D heterostructures with desired structures. Finally, potential opportunities are summarized concerning future developments in this emerging field, including (1) methods for the large-area production of 2D heterostructures, (2) the fabrication of high-quality semiconductor heterojunction arrays, (3) the exploration of novel 2D heterostructures, (4) precious control of the twist angles between the components in vertical heterostructures, and (5) the fabrication of vertical multilayer heterostructures. We believe this review can point the way to the controllable growth of various 2D heterostructures for exploring novel physics and provide a scalable pathway to high-performance devices.

Controlled doping, as a cornerstone of the semiconductor industry, becomes one of the most important topics for two-dimensional (2D) semiconductors such as tungsten disulfide (WS2), with intriguing physical properties. Here, we present a facile, controllable and reversible strategy for surface charge transfer doping in the monolayer WS2 crystals. After triethylamine treatment, the field effect transistors (FETs) based on monolayer WS2 exhibit enhanced mobility up to 28.6 cm2 V−1 s−1, which is much larger than that of the pristine one (9.8 cm2 V−1 s−1). In addition, the n-doping via triethylamine treatment can also improve the photoresponsivity of the device, i.e. from pristine 6.4  ×  10−3 AW−1 to the doped 21 AW−1. Interestingly, the electron transport properties of the doped WS2 can be recovered to be close to that of the intrinsic WS2 via acetone immersion. Moreover, the electron doping and reversibility are evidently observed in Raman, photoluminscence, and x-ray photoelectron spectroscopy (XPS). The reversibility of electrical and optical modification holds potential for functional diversification of 2D devices.