The team led by Professor Lee Chul-ho developed a two-dimensional semiconductor quantum structure for atomic-level thin LEDs and lasers.
The team's paper is published in the world-renowned journal, Science Advances

▲ Professor Lee Chul-ho of the KU-KIST Graduate School (left, corresponding author), 

Kim Yoon-seok, Integrated Master's and Doctoral Program (right, first author)

The research team led by Professor Lee Chul-Ho (Kim Yoon-seok, Integrated Master's and Doctoral Program) of the KU-KIST Graduate School of Converging Science and Technology at Korea University, through joint research with Professor Lee Kwan-hyung of the Department of Materials Science and Engineering at Seoul National University, developed a source technology for the future implementation of high-efficiency LEDs and lasers with atomic-level thickness by fabricating a two-dimensional transition metal chalcogenide-based multiple quantum well structure. This achievement is attracting attention as a next-generation semiconductor.

The research team used layered tungsten diselenide (WSe2), a two-dimensional semiconductor material that is in the spotlight as a candidate material for next-generation high-efficiency light-emitting devices and quantum light sources, to develop a monolithic bandgap control technology through a single-layer oxidation process to implement a heterojunction between the atomically thin quantum barrier layer (WOX) and the quantum well layer (WSe2) in one material. In addition, it was proven that the luminescence efficiency improved as the number of quantum wells increased in a multiple quantum well structure in which this junction structure was repeated periodically. In particular, the strong confinement effect of excitons and the rapid recombination behavior of excitons were experimentally proven by confirming that the luminescence intensity of the triple quantum well structure improved five times compared to the single quantum well structure.

* Quantum well: One of the heterojunction structures formed by continuously alternating semiconductors with relatively large band gaps and small semiconductors. It is used to increase the luminous efficiency of devices such as LEDs and lasers by effectively confining electrons and holes in the quantum well layer in this structure to maximize the confinement effect of excitons (electron-hole bonding pair)

(Figure top) A schematic diagram and cross-sectional photograph of a two-dimensional semiconductor-based multi-quantum well structure and band structure
(Figure bottom) Measurement of photoluminescence intensity, spectrum and exciton recombination time according to the number of quantum wells

In the case of conventional layered 2D semiconductors, if the number of layers of material is increased to amplify the volume of the light emitting active layer, the band structure changes from a direct transition type to an indirect transition type, resulting in a fundamental decrease in luminescence efficiency and forms a quantum barrier to the 2D semiconductor. Difficulties existed in the absence of suitable materials that could be used as layers. To solve this problem, the research team introduced a new ‘monolithic bandgap control methodology' that could implement a quantum well structure with an ideal interface by simultaneously forming a quantum well layer and a barrier layer in one material through a single-layer oxidation process of a two-dimensional semiconductor. It is of academic and technical significance as it overcomes the limitations of the development of high-efficiency light-emitting devices based on 2D semiconductors by using several single layers as active layers without deteriorating light-emitting performance. The results of this study will enable the development of high-efficiency quantum light-emitting devices as well as ultra-thin optoelectronic devices in a transparent and flexible form. These results are expected to have great technological and industrial ripple effects in the future, such as in optoelectronic circuits, displays, and mobile/wearable electronic devices.

The study, highly recognized for overcoming the technical limitations in implementing 2D semiconductor-based quantum structures and suggesting new application possibilities as a next-generation high-efficiency light emitting device, was published on March 26 in Science Advances (Impact Factor: 13.16), a sister journal of the world-renowned academic journal Science. The research was supported by the Samsung Research Funding Center of Samsung Electronics (Project Number: SRFC-MA1502-12), National Research Foundation of Korea (NRF-2017R1A5A1014862 (SRC Program: vdWMRC Center), 2020R1A2C2009389), and KU-KIST School Project.

The research team was led by Professor Lee Chul-ho (Kim Yoon-seok, Integrated Master's and Doctoral Program) of the KU-KIST Graduate School of Converging Science and Technology at Korea University in close cooperation with the research team of Professor Lee Gwan-hyoung of the Department of Materials Science and Engineering at Seoul National University (Kang So-jung, Integrated Master's and Doctoral Program) with Professor Park Hong-gyu from Korea University, Professor Jeong Hu-young (Ulsan National Institute of Science and Technology (UNIST)), Professor Cheong Hyeon-sik (Sogang University) and Professor Park Jin-woo (Yonsei University) participating in the joint research.
* Paper title: Atomic layer–confined multiple quantum wells enabled by monolithic bandgap engineering of transition metal dichalcogenide, Sci, Adv. 7, eabd7921
* Author information: A total of 16 researchers contributed, including Kim Yoon-seok (Korea University, first author), Kang So-jung (Yonsei University, co-first author), Professor Park Jin-woo (Yonsei University, co-author), Professor Cheong Hyeon-sik (Sogang University, co-author), Professor Jeong Hu-young (UNIST, co-author), Professor Park Hong-gyu (Korea University, co-author), Professor Lee Gwan-Hyoung (Seoul National University, corresponding author), and Professor Lee Chul-ho (Korea University, corresponding author),