Ultrafast growth of large single crystals of monolayer WS2 and WSe2.

Zhengwei Zhang,Bei Zhao,Peng Chen,Yuan Liu,Xiangdong Yang,Xidong Duan,Huifang Ma,Xiangfeng Duan,Jun Luo,Jia Li

doi:10.1093/nsr/nwz223

Abstract

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.

Highlights

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention for their distinct physical properties, such as atomically thin geometry, extraordinary mechanical flexibility, layer-number dependent electronic and optoelectronic properties, and tunable spin and valley polarization [1,2,3,4], and their potential applications in 2D electronics, optoelectronics and spintronics [5,6,7,8,9,10,11,12,13,14]
The chemical vapor source is continuously generated and unintentionally supplied to the growth substrate during the temperature ramping stage. Such unintentional supply of the chemical vapor source leads to undesired nucleation and growth before reaching the optimum growth temperature. This makes it difficult to explore the use of a high growth temperature, because the higher the designated growth temperature, the greater the unintended chemical vapor supply before reaching the designated growth temperature, which leads to highly heterogeneous thin film deposition with poor control of the thickness and domain size (Fig. 1a–d)
To minimize excessive vapor supply and undesired material deposition during the temperature ramping stage, growth is typically carried out at a lower temperature (e.g.,

Summary

Introduction

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention for their distinct physical properties, such as atomically thin geometry, extraordinary mechanical flexibility, layer-number dependent electronic and optoelectronic properties, and tunable spin and valley polarization [1,2,3,4], and their potential applications in 2D electronics, optoelectronics and spintronics [5,6,7,8,9,10,11,12,13,14]. 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.

Results

Conclusion