Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > New semiconductor laser structure could produce more efficient, powerful and portable sources emitting in the mid-infrared

Professors Dan Botez and Luke Mawst
Professors Dan Botez and Luke Mawst

Abstract:
University of Wisconsin-Madison researchers have achieved a nanoscale laser structure they anticipate will produce semiconductor lasers in the next two years that are more than twice as efficient as current continuous-wave lasers emitting in the mid-infrared.

New semiconductor laser structure could produce more efficient, powerful and portable sources emitting in the mid-infrared

Madison, WI | Posted on December 8th, 2009

"The novel structure will produce lasers with more power and that are more efficient, reliable and stable," says Philip Dunham Reed Professor of Electrical and Computer Engineering Dan Botez, who created the new structure with Electrical and Computer Engineering Professor Luke Mawst.

These next-generation lasers could benefit a wide range of industries, as they could be used in biomedical devices, environmental monitoring devices, missile avoidance systems and even food packaging processes. This wide range of applications is possible because the researchers have all but eliminated the temperature sensitivity for lasers operating in continuous-wave mode, meaning the laser emits uninterrupted, coherent light.

"For example, with current mid-infrared technologies for detecting explosives, lasers can detect from only approximately 30 feet away," Botez says. "With these lasers, devices could detect explosives at more like 300 feet away."

Also important is that the researchers created the new laser structure via a scalable industrial process.

How is a regular semiconductor laser built?

Researchers can harness electron movement to produce a laser. In a free-floating atom, electrons orbit in rings closer to or farther from the nucleus, depending on how much energy the electron is carrying. In a solid, atoms are fixed in a lattice (like a complex chain or pattern), and electrons move in and jump between energy bands instead of between the fixed energy levels corresponding to the various orbits in free atoms. In semiconducting materials, electrons can move into an energy band, called a conduction band, which produces a current. They can also move inside a band called a valence band that is so jam-packed with electrons that no net current flow happens. Electrons can easily be stimulated to move to the conduction band—but to maintain equilibrium, they eventually have to return to the valence band to fill in the "holes". they left behind. The electron returns to the valence band via a port or "well" in the conduction band, which dips closer to the valence band in a region called the "active region". As that occurs, the electron gives off its excess energy, sometimes in the form of a photon, which is a quantum of light. (A quantum of something is the smallest discrete quantity possible.)

Electrons that spontaneously move between bands and produce light can be used for devices like LEDs. However, to produce a laser beam, researchers place the lattice of atoms in a cavity with mirrors, and the generated photons stimulate the electrons to return to the valence band, thus releasing a photon with the same energy as the stimulating one. The original photon and the new photon are in phase with each other and will further stimulate the release of other photons, thus continuously amplifying the number of photons and bouncing off the cavity mirrors. The process repeats until the cavity reaches a threshold for oscillation and light is directed out of the cavity in a coherent laser beam.

This is how a standard semiconductor laser works, but the problem is that band-to-band transitions are limited to wavelengths below approximately three microns, which correspond to transition energies of about .4 electron volts. If the transition energies are smaller, which would correspond to longer wavelengths, the energy is released as heat, rather than light—meaning traditional semiconductor lasers have limited emitted-light wavelength potential.

A move forward: quantum cascade lasers

To overcome wavelength limitations, scientists from Bell Laboratories developed a laser by quantizing the energy bands, meaning they broke the energy bands into sub-bands. As the lattice structure vibrates, it causes the electrons to move rapidly between sub-bands, and the transitions between sub-bands cause the electrons to emit energy. However, the process is extremely inefficient since electrons transitioning between two sub-bands emit 1,000 phonons (quantized lattice vibrations) for every one photon. Bell Labs scientists reduced this inefficiency by creating a "cascade" structure by .stacking. 40 sub-band photon-emitting stages. These stages allow one electron to be used to emit a photon 40 times as it sequentially moves and transitions along the cascade structure. The result is only 25 phonons are emitted for every one emitted photon and then lasing action can be achieved.

The problem with this type of laser is that fixed compositions of the layers for a particular stage, which repeats along the cascade structure, result in electrons escaping from the structure. Imagine dropping a ball down a ladder; the ball may hit the first couple of steps, or sub-bands, but as it progresses along the ladder, it can veer off course and drop off the ladder entirely. A continuous-wave laser system, which operates continuously, heats up internally as electrons escape from the structure, which in turn limits the emitted power and the overall device efficiency.

This loss of electrons, or carrier leakage, has been a major barrier to increasing laser efficiency for practical applications.

A solution: Deep-well quantum cascade lasers

About five years ago, a process for growing multi-layer semiconductor structures became available for fabricating quantum-cascade lasers. Called metalorganic chemical vapor deposition (MOCVD), the process is scalable, unlike previous crystal growth techniques suited for laboratories but not manufacturers. MOCVD involves exposing a substrate to high heat and chemicals, causing layers to form on the substrate in an atomic-lattice configuration. Unlike previous crystal-growth techniques, MOCVD allows researchers to fabricate cascade-laser structures with stages composed of layers of varying composition.

Botez and Mawst are using the MOCVD process to grow varying-composition structures that prevent carrier leakage. To compensate for the added strain caused in the structure by creating deeper (quantum) wells, they also create taller barriers. Now, rather than electrons escaping from the system like balls falling off a ladder, the system works like a set of tiered boxes, with a ball getting caught at each stage. This ensures that electrons will efficiently produce photons in every stage of the cascade structure. The new structure is called a deep-well quantum cascade laser.

"By suppressing carrier leakage, there is about 2.5 times less heating in the device while the laser is in continuous-wave operation," says Botez. "This is a dramatic improvement that means the device will be almost temperature insensitive".

The result will be continuous-wave lasers that Botez anticipates will achieve at least 20 percent wall-plug efficiency, which is the electrical-to-optical power efficiency of a laser system. Twenty percent efficiency would be roughly double the current world record for practical continuous-wave quantum cascade lasers.

This new structure, coupled with the fact that MOCVD is a process suitable for mass production, means that optimized mid-infrared lasers can become much more widespread in medicine, the military and a wide variety of industries.

"The effect will be that as you get more continuous wave power you should also get better long-term reliability and stability, because these lasers will be much less sensitive to temperature variations than conventional quantum cascade lasers," Botez says.

Botez and Mawst are actively interested in commercializing the technology, which is covered by two issued and one pending U.S. patents through the Wisconsin Alumni Research Foundation.

####

For more information, please click here

Copyright © University of Wisconsin-Madison College of Engineering

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Tunable diamond string may hold key to quantum memory: A process similar to guitar tuning improves storage time of quantum memory May 24th, 2018

Remote control of transport through nanopores: New study outlines key factors affecting the transfer of molecules through biological channels May 24th, 2018

2018 Kavli Prizes in Astrophysics, Nanoscience, and Neuroscience to be Announced Live on May 31: Live announcement at the Norwegian Academy of Science and Letters to be streamed live at World Science Festival Event May 24th, 2018

'Spooky action at a distance': Researchers develop module for quantum repeater May 23rd, 2018

Possible Futures

Tunable diamond string may hold key to quantum memory: A process similar to guitar tuning improves storage time of quantum memory May 24th, 2018

Remote control of transport through nanopores: New study outlines key factors affecting the transfer of molecules through biological channels May 24th, 2018

'Spooky action at a distance': Researchers develop module for quantum repeater May 23rd, 2018

Columbia Researchers Squeeze Light into Nanoscale Devices and Circuits: Team is first to directly image propagation and dynamics of graphene plasmons at very low temperatures; findings could impact optical communications and signal processing May 23rd, 2018

Announcements

Tunable diamond string may hold key to quantum memory: A process similar to guitar tuning improves storage time of quantum memory May 24th, 2018

Remote control of transport through nanopores: New study outlines key factors affecting the transfer of molecules through biological channels May 24th, 2018

2018 Kavli Prizes in Astrophysics, Nanoscience, and Neuroscience to be Announced Live on May 31: Live announcement at the Norwegian Academy of Science and Letters to be streamed live at World Science Festival Event May 24th, 2018

'Spooky action at a distance': Researchers develop module for quantum repeater May 23rd, 2018

Homeland Security

The dispute about the origins of terahertz photoresponse in graphene results in a draw April 26th, 2018

Graphene origami as a mechanically tunable plasmonic structure for infrared detection April 25th, 2018

Nuclear radiation detecting device could lead to new homeland security tool: New device can detect gamma rays and identify radioactive isotopes April 25th, 2018

A dash of gold improves microlasers: The precious metal provides a 'nano' solution for improving disease detection, defense and cybersecurity applications October 9th, 2017

Military

Tunable diamond string may hold key to quantum memory: A process similar to guitar tuning improves storage time of quantum memory May 24th, 2018

Columbia Researchers Squeeze Light into Nanoscale Devices and Circuits: Team is first to directly image propagation and dynamics of graphene plasmons at very low temperatures; findings could impact optical communications and signal processing May 23rd, 2018

Hematene joins parade of new 2D materials: Rice University-led team extracts 3-atom-thick sheets from common iron oxide May 8th, 2018

Engineered polymer membranes could be new option for water treatment May 6th, 2018

Food/Agriculture/Supplements

HTA to Present European Strategy for Competitive Micro- and Nanotechnologies & Smart Systems: Special Event in Brussels on April 24 Gathers Research Institutes’ CEOs, European Commissioners and Key European Industrials April 17th, 2018

Twisting laser light offers the chance to probe the nano-scale: A new method to sensitively measure the structure of molecules has been demonstrated by twisting laser light and aiming it at miniscule gold gratings to separate out wavelengths: April 5th, 2018

Graphene on toast, anyone? Rice University scientists create patterned graphene onto food, paper, cloth, cardboard February 13th, 2018

Silk fibers could be high-tech ‘natural metamaterials’ January 31st, 2018

Environment

Engineered polymer membranes could be new option for water treatment May 6th, 2018

Harvesting clean hydrogen fuel through artificial photosynthesis May 3rd, 2018

'Sweet spot' in sweet material for hydrogen storage: Study IDs 'white graphene' architecture with unprecedented hydrogen storage capacity March 12th, 2018

Converting CO2 into Usable Energy: Scientists show that single nickel atoms are an efficient, cost-effective catalyst for converting carbon dioxide into useful chemicals March 1st, 2018

Nanobiotechnology

Remote control of transport through nanopores: New study outlines key factors affecting the transfer of molecules through biological channels May 24th, 2018

New blood test rapidly detects signs of pancreatic cancer May 17th, 2018

Nanomedicine -- Targeting cancer cells with sugars May 14th, 2018

NanoBio Announces Corporate Name Change to BlueWillow Biologics and Closes $10M Series A Financing: Move Reflects Focus on Advancing Several Intranasal Vaccines to Human Studies May 9th, 2018

Photonics/Optics/Lasers

Columbia Researchers Squeeze Light into Nanoscale Devices and Circuits: Team is first to directly image propagation and dynamics of graphene plasmons at very low temperatures; findings could impact optical communications and signal processing May 23rd, 2018

A micro-thermometer to record tiny temperature changes May 15th, 2018

Strain improves performance of atomically thin semiconductor material May 11th, 2018

A powerful laser breakthrough: Lehigh research team demonstrates terahertz semiconductor laser with record-high output power May 2nd, 2018

Quantum nanoscience

Nanoscale measurements 100x more precise, thanks to improved two-photon technique May 8th, 2018

'Exceptional' research points way toward quantum discoveries: Rice University scientists make tunable light-matter couplings in nanotube films April 30th, 2018

New qubit now works without breaks: A universal design for superconducting qubits has been created April 19th, 2018

Quantum shift shows itself in coupled light and matter: Rice University scientists corral, quantify subtle movement in condensed matter system April 16th, 2018

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project