| 초록 |
Two dimensional (2D) materials and their van der Waals (vdW) heterostructures, weakly combined atomic layers by van der Waals force, have attracted extensive interests because of their unique properties and large degree of freedom in design of new materials. In particular, electronic devices based on vdW heterostructures are promising because novel devices with unprecedented functions can be fabricated in a few atomic thickness. However, there are critical issues to be overcome for practical applications of 2D materials. For device applications, stacking technique, high contact resistance, and stacking angle control should be improved. Here I present novel contact engineering strategies for vdW heterostructure devices. Graphene can be used as etch masks and etch stops in XeF2 etching process of vdW heterostructures. By using graphene etch masks, we fabricated low resistance via contacts to graphene embedded in hexagonal boron nitride (hBN), leading to extremely small contact resistance ultrahigh mobility. This technique can be used for integration of vertically stacked graphene devices and connecting vias of embedded graphene leads. As a light emitting device, we demonstrate light-emitting transistors of WSe2 with gate-tunable graphene contacts and light-emitting tunnel devices based on vdW heterostructure by utilizing quantum confinement in vertically stacked 2D semiconductor for higher efficiency. By modulating Schottky barrier of graphene-WSe2 interface, two different types of carriers can be controllably injected to light emitting layer of WSe¬2. Hence, WSe2 emits a light by recombination of separately injected holes and electrons. In the light-emitting tunnel devices, concentration of trions, negatively charged excitons, is modulated by using additional charge injection electrode. This work shows high tunability of charged excitons in vdW optoelectronic devices, which cannot be achieved in conventional semiconductor devices. Our work great promise toward highly integrated 2D devices with extraordinary optoelectronic functions. |
