13:30 〜 15:30
▼ [5p-PA1-68] Hydrogen-Induced Epitaxial Growth of Monolayer WS2 and Orientation-Dependent Grain Boundaries
キーワード：Epitaxial growth, Grain Boundary, Tungsten disulfide
Transition metal dichalcogenides (TMDCs) have been attracting a great interest, because they have a finite band gap, high mobility, and mechanical flexibility which promise applications in flexible electronics and optoelectronics. For such applications, chemical vapor deposition (CVD) is a powerful method, because it enables the large-scale growth with relatively low cost. However, in the standard CVD system using Ar carrier gas, TMDC grains are randomly oriented and a multilayer grain exists at the center of each grain, resulting in degraded device performance. Therefore, it is very important to develop a new method to grow multilayer-free monolayer TMDCs with controlled grain orientation.
In this work, we demonstrate that high concentration of hydrogen gas in the CVD process enhances the interaction between WS2 and sapphire surface, resulting in the highly aligned WS2 grains. This work compares the WS2 grains obtained by the standard CVD with Ar gas and our method using high concentration of H2. It is clearly seen that WS2 grains are oriented, registered by the underlying the sapphire surface. In addition, the AFM measurements revealed that the WS2 grains grown with H2 have no multilayer grains at the center of monolayer grains. Photoluminescence (PL) quenching was observed, reflecting strong coupling between the WS2 and the substrate. Result shows scanning transmission electron microscopy (STEM) images of interfaces between two merged grains. The misaligned WS2 showed various kinds of GB structures depending on misalign angles. On the other hand, the aligned WS2 grains possessed unique dislocations with less point defects and impurities. Finally, field-effect transistors (FETs) were fabricated to understand the influence of GBs on the carrier transport property. The conductance degradation across GBs observed in the misoriented WS2 grains was not seen for the oriented WS2, suggesting the importance of the controlling the grain orientation for obtaining high device performance. Our work offers a new approach to control the WS2 orientation, which will accelerate the potential applications of 2D materials.
In this work, we demonstrate that high concentration of hydrogen gas in the CVD process enhances the interaction between WS2 and sapphire surface, resulting in the highly aligned WS2 grains. This work compares the WS2 grains obtained by the standard CVD with Ar gas and our method using high concentration of H2. It is clearly seen that WS2 grains are oriented, registered by the underlying the sapphire surface. In addition, the AFM measurements revealed that the WS2 grains grown with H2 have no multilayer grains at the center of monolayer grains. Photoluminescence (PL) quenching was observed, reflecting strong coupling between the WS2 and the substrate. Result shows scanning transmission electron microscopy (STEM) images of interfaces between two merged grains. The misaligned WS2 showed various kinds of GB structures depending on misalign angles. On the other hand, the aligned WS2 grains possessed unique dislocations with less point defects and impurities. Finally, field-effect transistors (FETs) were fabricated to understand the influence of GBs on the carrier transport property. The conductance degradation across GBs observed in the misoriented WS2 grains was not seen for the oriented WS2, suggesting the importance of the controlling the grain orientation for obtaining high device performance. Our work offers a new approach to control the WS2 orientation, which will accelerate the potential applications of 2D materials.