. 24/7 Space News .
CHIP TECH
The thinnest photodetector in the world
by Staff Writers
Seoul, South Korea (SPX) Nov 14, 2016


(a) Illustration of the device with the molybdenum disulfide (MoS2) semiconductor layer sandwiched between top (GrT) and bottom (GrB) graphene layers. Light (green ray) is absorbed and converted into an electric current. When light is absorbed by the device, electrons (blue) jump into a higher energy state and holes (red) are generated in the MoS2 layer. The movement of holes and electrons created by the difference in electronic potential between the GrT-MoS2 and the GrB-MoS2 junctions generates the electric current. Image courtesy IBS. For a larger version of this image please go here.

The Center for Integrated Nanostructure Physics, within the Institute for Basic Science (IBS) has developed the world's thinnest photodetector, that is a device that converts light into an electric current. With a thickness of just 1.3 nanometers - 10 times smaller than the current standard silicon diodes - this device could be used in the Internet of Things, smart devices, wearable electronics and photoelectronics. This 2D technology, published on Nature Communications, uses molybdenum disulfide (MoS2) sandwiched in graphene.

Graphene is a fantastic material: It's conductive, thin (just one-atom thick), transparent and flexible. However, since it does not behave as a semiconductor, its application in the electronics industry is limited. Therefore, in order to increase graphene's usability, IBS scientists sandwiched a layer of the 2D semiconductor MoS2 between two graphene sheets and put it over a silicon base. They initially thought the resulting device was too thin to generate an electric current but, unexpectedly, it did.

"A device with one-layer of MoS2 is too thin to generate a conventional p-n junction, where positive (p) charges and negative (n) charges are separated and can create an internal electric field. However, when we shine light on it, we observed high photocurrent. It was surprising! Since it cannot be a classical p-n junction, we thought to investigate it further," explains YU Woo Jong, first author of this study.

To understand what they found, the researchers compared devices with one and seven layers of MoS2 and tested how well they behave as a photodetector, that is, how they are able to convert light into an electric current. They found that the device with one-layer MoS2 absorbs less light than the device with seven layers, but it has higher photoresponsitivity.

"Usually the photocurrent is proportional to the photoabsorbance, that is, if the device absorbs more light, it should generate more electricity, but in this case, even if the one-layer MoS2 device has smaller absorbance than the seven-layer MoS2, it produces seven times more photocurrent," describes Yu.

Why is the thinner device working better than the thicker one? The research team proposed a mechanism to explain why this is the case. They recognized that the photocurrent generation could not be explained with classical electromagnetism, but could be with quantum physics. When light hits the device, some electrons from the MoS2 layer jump into an excited state and their flow through the device produces an electric current. However in order to pass the boundary between MoS2 and graphene, the electrons need to overcome an energy barrier (via quantum tunnelling), and this is where the one-layer MoS2 device has an advantage over the thicker one.

The monolayer is thinner and therefore more sensitive to the surrounding environment: The bottom SiO2 layer increases the energy barrier, while the air on top reduces it, thus electrons in the monolayer device have a higher probability to tunnel from the MoS2 layer to the top graphene (GrT).

The energy barrier at the GrT/MoS2 junction is lower than the one at the GrB/MoS2, so the excited electrons transfer preferentially to the GrT layer and create an electric current. Conversely, in the multi-layer MoS2 device, the energy barriers between GrT/MoS2 and GrB/MoS2 are symmetric, therefore the electrons have the same probability to go either side and thus reduce the generated current.

Imagine a group of people in a valley surrounded by two mountains. The group wants to get to the other side of the mountains, but without making too much effort. In one case ( the seven-layers MoS2 device), both mountains have the same height so whichever mountain is crossed, the effort will be the same. Therefore half the group crosses one mountain and the other half the second mountain.

In the second case (analogue to the one-layer MoS2 device), one mountain is taller than the other, so the majority of the group decide to cross the smaller mountain. However, because we are considering quantum physics instead of classical electromagnetism, they do not need to climb the mountain until they reach the top (as they would need to do with classical physics), but they can pass through a tunnel.

Although electron tunneling and walking a tunnel in a mountain are very different of course, the idea is that electric current is generated by the flow of electrons, and the thinner device can generate more current because more electrons flow towards the same direction.

Actually, when light is absorbed by the device and MoS2 electrons jump into an excited state, they leave the so-called holes behind. Holes behave like positive mobile charges and are essentially positions left empty by electrons that absorbed enough energy to jump to a higher energy status. Another problem of the thicker device is that electrons and holes move too slowly through the junctions between graphene and MoS2, leading to their undesired recombination within the MoS2 layer.

For these reasons, up to 65% of photons absorbed by the thinner device are used to generate a current. Instead, the same measurement (quantum efficiency) is only 7% for the seven-layer MoS2 apparatus.

"This device is transparent, flexible and requires less power than the current 3D silicon semiconductors. If future research is successful, it will accelerate the development of 2D photoelectric devices," explains the professor.

Research paper


Comment on this article using your Disqus, Facebook, Google or Twitter login.


Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor
$5 Billed Once


credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly


paypal only


.


Related Links
Institute for Basic Science
Computer Chip Architecture, Technology and Manufacture
Nano Technology News From SpaceMart.com






Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Previous Report
CHIP TECH
Researchers discover new method to dissipate heat in electronic devices
Riverside CA (SPX) Nov 14, 2016
Controlling the flow of heat through semiconductor materials is an important challenge in developing smaller and faster computer chips, high-performance solar panels, and better lasers and biomedical devices. For the first time, an international team of scientists led by a researcher at the University of California, Riverside has modified the energy spectrum of acoustic phonons - elemental ... read more


CHIP TECH
Russian New Generation Satellites to Undergo First Flight Tests in 2020

NASA, U.S. Navy Practice Orion Recovery Procedures

Russia space center to work with US on spaceflight biomed issues

Progress, but uphill slog for women in tech

CHIP TECH
Ariane 5 at launch zone for Nov 17 mission with four Galileo satellites

Airbus Safran Launchers and ESA sign confirmation of the Ariane 6 program

US revives hypersonic aerospace research

JCSAT-15 arrives in Kourou for Dec Ariane 5 launch

CHIP TECH
Can we grow potatoes on Mars

Dutch firm unveils concept space suit for Mars explorers

Meteorites reveal lasting drought on Mars

Opportunity heads to next waypoint at over 27 miles on the odometer

CHIP TECH
China launches pulsar test satellite

China's Chang'e-2 a success

Long March-5 reflects China's "greatest advancement" yet in rockets

New heavy-lift carrier rocket boosts China's space dream

CHIP TECH
Can India beat China at its game with common satellite for South Asia

SSL delivers powerful, high capacity broadband satellite for Hughes to Cape Canaveral

NASA to Launch Fleet of Hurricane-Tracking SmallSats

NASA small satellites will take a fresh look at Earth

CHIP TECH
Scientists have 'scared away' microparticles with laser light

Study: Math scares everyone, even physicists

Exotic property of salty solutions discovered

Tiny magnifying glass reveals chemical bonds between atoms

CHIP TECH
Earth-bound instrument analyzes light from planets circling distant stars

Protoplanetary Discs Being Shaped by Newborn Planets

Scientists unveil latest exoplanet-hunter CHARIS

What happens to a pathogenic fungus grown in space?

CHIP TECH
Mystery solved behind birth of Saturn's rings

Last Bits of 2015 Pluto Flyby Data Received on Earth

Uranus may have two undiscovered moons

Possible Clouds on Pluto, Next Target is Reddish









The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.