Yoon Seok Kim1,Sojung Kang2,Jaepil So1,Jong Chan Kim3,Kangwon Kim4,Seunghoon Yang1,Yeonjoon Jung5,Yongjun Shin5,Seongwon Lee1,Donghun Lee1,Jin-Woo Park2,Hyeonsik Cheong4,Hu Young Jeong3,Hong-Gyu Park1,Gwan-Hyong Lee5,Chul-Ho Lee1
Korea University1,Yonsei University2,Ulsan National Institute of Science and Technology3,Sogang University4,Seoul National University5
Yoon Seok Kim1,Sojung Kang2,Jaepil So1,Jong Chan Kim3,Kangwon Kim4,Seunghoon Yang1,Yeonjoon Jung5,Yongjun Shin5,Seongwon Lee1,Donghun Lee1,Jin-Woo Park2,Hyeonsik Cheong4,Hu Young Jeong3,Hong-Gyu Park1,Gwan-Hyong Lee5,Chul-Ho Lee1
Korea University1,Yonsei University2,Ulsan National Institute of Science and Technology3,Sogang University4,Seoul National University5
Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) have attracted enormous attention because of exceptional optical properties such as large exciton binding energy, and strong light-matter interaction at the ultimate thickness limit. Such remarkable properties make them promising for high-performance light-emitting devices such as LEDs, LASERs, and single-photon emitters. However, high efficiency in the luminescence of those 2D semiconductors is inherently limited to monolayer regime due to indirect-to-direct bandgap transition. In addition, a quantum well (QW) structure for luminescence enhancement is hard to be implemented by using semiconductor TMDs as a light-emitting layer due to a lack of large bandgap materials for construction of type-I band alignment and facile fabrication methods compatible with these atomically thin materials. In this regard, a facile fabrication of the TMDs-based multiple quantum wells (MQWs) that enables for both confining excitons and enlarging active volume remains a considerable challenge.<br/>Here, we demonstrate the novel approach to fabricate atomic-layer-confined MQWs via monolithic bandgap engineering of TMDs and artificial van der Waals stacking. A fundamental building block of QWs, the WO<sub>X</sub>/WSe<sub>2</sub> hetero-bilayer, was prepared by monolithic oxidation of the WSe<sub>2</sub> bilayer, followed by stacking the blocks into the MQWs. By examining the band alignment of WO<sub>X</sub>/WSe<sub>2</sub>, we confirm that the hetero-bilayer WO<sub>X</sub>/WSe<sub>2</sub> constructs the type-I quantum well for efficient exciton confinement and radiative recombination. Unlike the case of stacking monolayers only, the super-linear increases of photoluminescence with the number of QWs were achieved: about 5-fold enhancement for triple QWs. Furthermore, the quantum-confined radiative recombination in MQWs was verified by a large exciton binding energy of 193 meV and a short exciton lifetime of 170 ps. This work paves the way toward monolithic integration of 2D superlattices for novel quantum optoelectronics.