Nav: Home

Quantum dots amplify light with electrical pumping

November 20, 2017

LOS ALAMOS, N.M., November 20, 2017-- In a breakthrough development, Los Alamos scientists have shown that they can successfully amplify light using electrically excited films of the chemically synthesized semiconductor nanocrystals known as quantum dots. The quantum dot films are integrated into devices much like the now-ubiquitous light-emitting diodes (LEDs), but, in this case designed to sustain the high current densities required for achieving the optical-gain regime. One sees laser diodes every day in laser pointers, barcode readers and the like, and a key element of such devices is an optical-gain medium, which instead of absorbing incident light, amplifies it.

"Optical gain with electrically excited quanum dots is now a reality," said Victor Klimov, head of the quantum dot team at Los Alamos. "We have been working to develop new lasing media, using chemically synthesized quantum dots, although it had been widely believed that quantum dot lasing with electrical stimulation is simply impossible," he said. "By using our specially designed dots, we can avoid energy losses created by Auger recombination."

New lasers, made more efficiently

These results demonstrate the feasibility of a new generation of highly flexible, electrically pumped lasers processible from solutions that can complement or even eventually displace existing laser diodes fabricated using more complex and costly vacuum-based epitaxial techniques. These prospective devices can enable a variety of applications, from RGB laser modules for displays and projectors, to multi-wavelength micro-lasers for biological and chemical diagnostics.

Designer Dots With No Heat Loss

In the new report published today in Nature Materials , the Los Alamos team demonstrates that using their "designer" quantum dots, they can achieve light amplification in a nanocrystal solid with direct-current electrical pumping. The key property of the novel quantum dots, underlining the success of the conducted study, is a carefully engineered particle interior in which the material's composition is continuously varied along a radial direction. This approach eliminates sharp steps in the atomic composition which would normally trigger Auger recombination. As a result, the engineered quantum dots feature nearly complete suppression of Auger effect's heat loss, and this allows for redirecting the energy released by the electrical current into the light-emission channel instead of wasteful heat.

The Los Alamos nanotechnology team originally discovered the lasing effect in semiconductor nanocrystals in 2000. In these proof-of-principle experiments, reported in the journal Science, the quantum dots were stimulated with very short (femtosecond) laser pulses used to outcompete optical gain decay caused by the Auger process. Short optical gain lifetimes create an especially serious problem in the case of electrical pumping, which is an inherently slow process as electrons and holes are injected into the quantum dot one-by-one.

Staying focused

Another important element of this work is a special "current-focusing" device architecture which allows the high current densities necessary for achieving optical gain. The method used by Los Alamos researchers was to taper one of the charge-injection electrodes, limiting the size of the current-conducting area to less than 100 microns. Using this strategy, they were able to produce current concentration sufficient to reach the regime of light amplification without damaging either the dots or the injection layers.
-end-
Publication: Jaehoon Lim, Young-Shin Park, and Victor I. Klimov, Optical Gain in Colloidal Quantum Dots Achieved with Direct-Current Electrical Pumping, Nature Materials, http://dx.doi.org/0.1038/nmat5011.

Project members: Jaehoon Lim (Postdoctoral Research Associate), Young-Shin Park (Guest Scientist, UNM), Victor I. Klimov (Laboratory Fellow, Project Leader).

Acknowledgements: Spectroscopic studies and optical-gain and lasing modelling were funded by the U.S Department of Energy Office of Science. The work on the quantum dot synthesis and device fabrication was supported by the Laboratory Directed Research and Development program at Los Alamos National Laboratory.

About Los Alamos National Laboratory

Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is operated by Los Alamos National Security, LLC, a team composed of Bechtel National, the University of California, BWX Technologies, Inc. and URS Corporation for the Department of Energy's National Nuclear Security Administration.

Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health and global security concerns.

DOE/Los Alamos National Laboratory

Related Quantum Dots Articles:

'Growing' active sites on quantum dots for robust H2 photogeneration
Chinese researchers had achieved site- and spatial- selective integration of earth-abundant metal ions in semiconductor quantum dots (QDs) for efficient and robust photocatalytic H2 evolution from water.
New insights into the energy levels in quantum dots
Researchers from Basel, Bochum and Copenhagen have gained new insights into the energy states of quantum dots.
What a pair! Coupled quantum dots may offer a new way to store quantum information
Researchers at the National Institute of Standards and Technology (NIST) and their colleagues have for the first time created and imaged a novel pair of quantum dots -- tiny islands of confined electric charge that act like interacting artificial atoms.
Spinning quantum dots
A new paper in EPJ B presents a theoretical analysis of electron spins in moving semiconductor quantum dots, showing how these can be controlled by electric fields in a way that suggests they may be usable as information storage and processing components of quantum computers.
Controlling the charge state of organic molecule quantum dots in a 2D nanoarray
Australian researchers have fabricated a self-assembled, carbon-based nanofilm where the charge state (ie, electronically neutral or positive) can be controlled at the level of individual molecules.
Modified quantum dots capture more energy from light and lose less to heat
Los Alamos National Laboratory scientists have synthesized magnetically-doped quantum dots that capture the kinetic energy of electrons created by ultraviolet light before it's wasted as heat.
Using quantum dots and a smartphone to find killer bacteria
A combination of off-the-shelf quantum dot nanotechnology and a smartphone camera soon could allow doctors to identify antibiotic-resistant bacteria in just 40 minutes, potentially saving patient lives.
Synthesizing single-crystalline hexagonal graphene quantum dots
A KAIST team has designed a novel strategy for synthesizing single-crystalline graphene quantum dots, which emit stable blue light.
US Naval Research Laboratory 'connects the dots' for quantum networks
Researchers at the US Naval Research Laboratory developed a novel technique that could enable new technologies that use properties of quantum physics for computing, communication and sensing, which may lead to 'neuromorphic' or brain-inspired computing.
Quantum rebar: Quantum dots enhance stability of solar-harvesting perovskite crystals
Engineering researchers have combined two emerging technologies for next-generation solar power -- and discovered that each one helps stabilize the other.
More Quantum Dots News and Quantum Dots Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Listen Again: The Power Of Spaces
How do spaces shape the human experience? In what ways do our rooms, homes, and buildings give us meaning and purpose? This hour, TED speakers explore the power of the spaces we make and inhabit. Guests include architect Michael Murphy, musician David Byrne, artist Es Devlin, and architect Siamak Hariri.
Now Playing: Science for the People

#576 Science Communication in Creative Places
When you think of science communication, you might think of TED talks or museum talks or video talks, or... people giving lectures. It's a lot of people talking. But there's more to sci comm than that. This week host Bethany Brookshire talks to three people who have looked at science communication in places you might not expect it. We'll speak with Mauna Dasari, a graduate student at Notre Dame, about making mammals into a March Madness match. We'll talk with Sarah Garner, director of the Pathologists Assistant Program at Tulane University School of Medicine, who takes pathology instruction out of...
Now Playing: Radiolab

What If?
There's plenty of speculation about what Donald Trump might do in the wake of the election. Would he dispute the results if he loses? Would he simply refuse to leave office, or even try to use the military to maintain control? Last summer, Rosa Brooks got together a team of experts and political operatives from both sides of the aisle to ask a slightly different question. Rather than arguing about whether he'd do those things, they dug into what exactly would happen if he did. Part war game part choose your own adventure, Rosa's Transition Integrity Project doesn't give us any predictions, and it isn't a referendum on Trump. Instead, it's a deeply illuminating stress test on our laws, our institutions, and on the commitment to democracy written into the constitution. This episode was reported by Bethel Habte, with help from Tracie Hunte, and produced by Bethel Habte. Jeremy Bloom provided original music. Support Radiolab by becoming a member today at Radiolab.org/donate.     You can read The Transition Integrity Project's report here.