Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

'Odd couple' monolayer semiconductors align to advance optoelectronics

18.04.2016

Epitaxy, or growing crystalline film layers that are templated by a crystalline substrate, is a mainstay of manufacturing transistors and semiconductors. If the material in one deposited layer is the same as the material in the next layer, it can be energetically favorable for strong bonds to form between the highly ordered, perfectly matched layers. In contrast, trying to layer dissimilar materials is a great challenge if the crystal lattices don't match up easily. Then, weak van der Waals forces create attraction but don't form strong bonds between unlike layers.

In a study led by the Department of Energy's Oak Ridge National Laboratory, scientists synthesized a stack of atomically thin monolayers of two lattice-mismatched semiconductors. One, gallium selenide, is a "p-type" semiconductor, rich in charge carriers called "holes." The other, molybdenum diselenide, is an "n-type" semiconductor, rich in electron charge carriers.


Light drives the migration of charge carriers (electrons and holes) at the juncture between semiconductors with mismatched crystal lattices. These heterostructures hold promise for advancing optoelectronics and exploring new physics. The schematic's background is a scanning transmission electron microscope image showing the bilayer in atomic-scale resolution.

Credit: Oak Ridge National Laboratory, US Dept. of Energy. Image by Xufan Li and Chris Rouleau

Where the two semiconductor layers met, they formed an atomically sharp heterostructure called a p-n junction, which generated a photovoltaic response by separating electron-hole pairs that were generated by light. The achievement of creating this atomically thin solar cell, published in Science Advances, shows the promise of synthesizing mismatched layers to enable new families of functional two-dimensional (2D) materials.

The idea of stacking different materials on top of each other isn't new by itself. In fact, it is the basis for most electronic devices in use today. But such stacking usually only works when the individual materials have crystal lattices that are very similar, i.e., they have a good "lattice match." This is where this research breaks new ground by growing high-quality layers of very different 2D materials, broadening the number of materials that can be combined and thus creating a wider range of potential atomically thin electronic devices.

"Because the two layers had such a large lattice mismatch between them, it's very unexpected that they would grow on each other in an orderly way," said ORNL's Xufan Li, lead author of the study. "But it worked."

The group was the first to show that monolayers of two different types of metal chalcogenides--binary compounds of sulfur, selenium or tellurium with a more electropositive element or radical--having such different lattice constants can be grown together to form a perfectly aligned stacking bilayer. "It's a new, potential building block for energy-efficient optoelectronics," Li said.

Upon characterizing their new bilayer building block, the researchers found that the two mismatched layers had self-assembled into a repeating long-range atomic order that could be directly visualized by the Moiré patterns they showed in the electron microscope. "We were surprised that these patterns aligned perfectly," Li said.

Researchers in ORNL's Functional Hybrid Nanomaterials group, led by David Geohegan, conducted the study with partners at Vanderbilt University, the University of Utah and Beijing Computational Science Research Center.

"These new 2D mismatched layered heterostructures open the door to novel building blocks for optoelectronic applications," said senior author Kai Xiao of ORNL. "They can allow us to study new physics properties which cannot be discovered with other 2D heterostructures with matched lattices. They offer potential for a wide range of physical phenomena ranging from interfacial magnetism, superconductivity and Hofstadter's butterfly effect."

Li first grew a monolayer of molybdenum diselenide, and then grew a layer of gallium selenide on top. This technique, called "van der Waals epitaxy," is named for the weak attractive forces that hold dissimilar layers together. "With van der Waals epitaxy, despite big lattice mismatches, you can still grow another layer on the first," Li said. Using scanning transmission electron microscopy, the team characterized the atomic structure of the materials and revealed the formation of Moiré patterns.

The scientists plan to conduct future studies to explore how the material aligns during the growth process and how material composition influences properties beyond the photovoltaic response. The research advances efforts to incorporate 2D materials into devices.

For many years, layering different compounds with similar lattice cell sizes has been widely studied. Different elements have been incorporated into the compounds to produce a wide range of physical properties related to superconductivity, magnetism and thermoelectrics. But layering 2D compounds having dissimilar lattice cell sizes is virtually unexplored territory.

"We've opened the door to exploring all types of mismatched heterostructures," Li said.

The title of the paper is "Two-dimensional GaSe/MoSe2 misfit bilayer heterojunctions by van der Waals epitaxy."

###

Research, including materials synthesis, was supported by the DOE Office of Science. Materials characterization was conducted in part at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL. ORNL Laboratory Directed Research and Development funds supported some of the device measurements in the study.

UT-Battelle manages ORNL for DOE's Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time.

For more information, please visit www.science.energy.gov. --by Dawn Levy

CAPTION/CREDIT: Light drives the migration of charge carriers (electrons and holes) at the juncture between semiconductors with mismatched crystal lattices. These heterostructures hold promise for advancing optoelectronics and exploring new physics. The schematic's background is a scanning transmission electron microscope image showing the bilayer in atomic-scale resolution. Image credit: Oak Ridge National Laboratory, U.S. Dept. of Energy. Image by Xufan Li and Chris Rouleau

Media Contact

Dawn Levy
levyd@ornl.gov
865-576-6448

 @ORNL

http://www.ornl.gov 

Dawn Levy | EurekAlert!

More articles from Materials Sciences:

nachricht Argon is not the 'dope' for metallic hydrogen
24.03.2017 | Carnegie Institution for Science

nachricht Researchers make flexible glass for tiny medical devices
24.03.2017 | Brigham Young University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>