Atomic–layer–confined multiple quantum wells enabled by monolithic bandgap engineering of transition metal dichalcogenides

Abstract

Quantum wells (QWs), enabling effective exciton confinement and strong light-matter interaction, form an essential building block for quantum optoelectronics. For two-dimensional (2D) semiconductors, however, constructing the QWs is still challenging because suitable materials and fabrication techniques are lacking for bandgap engineering and indirect bandgap transitions occur at the multilayer. Here, we demonstrate an unexplored approach to fabricate atomic–layer–confined multiple QWs (MQWs) via monolithic bandgap engineering of transition metal dichalcogenides and van der Waals stacking. The WOX/WSe2 hetero-bilayer formed by monolithic oxidation of the WSe2 bilayer exhibited the type I band alignment, facilitating as a building block for MQWs. A superlinear enhancement of photoluminescence with increasing the number of QWs was achieved. Furthermore, 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 band-engineered heterostructures for 2D quantum optoelectronics.

Exciton Transfer at Heterointerfaces of MoS2 Monolayers and Fluorescent Molecular Aggregates

“…Transition metal dichalcogenides (TMDs) are 2D layered inorganic semiconductors that have the form of MX 2 compounds, in which the transition metal atom, M, is sandwiched between two chalcogen atoms, X. TMDs have attracted growing research attention for optoelectronic device applications since they have sizable bandgap energies (≈1.2–1.8 eV) and optical characteristics tunable by external stimuli, such as strain and electric/magnetic fields. [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ] TMD‐based heterostructures have been fabricated similar to conventional semiconductors. Energy band structure engineering at heterointerfaces enables control of the electrical transport and recombination of charge carriers in heterostructures.…”

“…Energy band structure engineering at heterointerfaces enables control of the electrical transport and recombination of charge carriers in heterostructures. [ 8 , 9 , 10 , 11 , 12 , 13 ] Among numerous TMDs, MoS 2 has been regarded as one of the strongest candidates for novel optoelectronic device applications. [ 8 , 9 , 10 , 11 , 12 , 14 , 15 , 16 , 17 ]…”

“…[ 8 , 9 , 10 , 11 , 12 , 13 ] Among numerous TMDs, MoS 2 has been regarded as one of the strongest candidates for novel optoelectronic device applications. [ 8 , 9 , 10 , 11 , 12 , 14 , 15 , 16 , 17 ]…”

“…Conjugated organic compounds have emerged as valuable active materials in a variety of devices, such as organic thin film transistors, solar cells, and organic light‐emitting devices (OLEDs). [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ] Their utility benefits from the high versatility in the design and synthesis of organic materials. For instance, recent advances have been made in OLEDs by taking advantage of the ability of molecules to accommodate transition metals or to spatially separate frontier orbitals.…”

“…[ 1 , 2 , 3 , 4 ] TMDs usually form type‐II band alignment, and charge transfer (CT) rather than exciton transfer (ET) is dominant at the interfaces. [ 9 , 10 , 11 , 12 , 13 , 14 , 15 ] Insertion of insulating layers between two TMD layers can suppress the interlayer CT process, and hence, the ET process enables enhanced light emission in TMD heterostructures. [ 14 , 15 ] Recent works have shown that combinations of suitable materials allow fabrication of both type‐I and type‐II organic/TMD heterojunctions.…”