Nanotechnology Now

Our NanoNews Digest Sponsors



Heifer International

Wikipedia Affiliate Button


android tablet pc

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

Iranian Experts Clean Uranium-Contaminated Water by Nano-Particles November 23rd, 2014

Novel Method Found for Connection of Metallic Alloys to Polymers November 23rd, 2014

New research project supports internationalisation in nano-research: Launch of new “Baltic Sea Network” November 22nd, 2014

3rd Iran-Proposed Nano Standard Approved by International Standard Organization November 22nd, 2014

Possible Futures

A novel method for identifying the body’s ‘noisiest’ networks November 19th, 2014

Researchers discern the shapes of high-order Brownian motions November 17th, 2014

VDMA Electronics Production Equipment: Growth track for 2014 and 2015 confirmed: Business climate survey shows robust industry sector November 14th, 2014

Open Materials Development Will Be Key for HP's Success in 3D Printing: HP can make a big splash in 3D printing, but it needs to shore up technology claims and avoid the temptation of the razor/razor blade business model in order to flourish November 11th, 2014

Announcements

Iranian Experts Clean Uranium-Contaminated Water by Nano-Particles November 23rd, 2014

Novel Method Found for Connection of Metallic Alloys to Polymers November 23rd, 2014

New research project supports internationalisation in nano-research: Launch of new “Baltic Sea Network” November 22nd, 2014

3rd Iran-Proposed Nano Standard Approved by International Standard Organization November 22nd, 2014

Homeland Security

Better bomb-sniffing technology: University of Utah engineers develop material for better detectors November 4th, 2014

Microrockets fueled by water neutralize chemical and biological warfare agents October 29th, 2014

NanoTechnology for Defense (NT4D) October 22nd, 2014

UT Arlington researchers develop transparent nanoscintillators for radiation detection for medical safety and homeland security September 29th, 2014

Military

NRL Scientists Discover Novel Metamaterial Properties within Hexagonal Boron Nitride November 20th, 2014

Two sensors in one: Nanoparticles that enable both MRI and fluorescent imaging could monitor cancer, other diseases November 18th, 2014

Researchers create & control spin waves, lifting prospects for enhanced info processing November 17th, 2014

Penn engineers efficiently 'mix' light at the nanoscale November 17th, 2014

Food/Agriculture/Supplements

Production of Biodegradable Nanocomposites of Wheat Gluten in Iran November 6th, 2014

New tool could help reshape the limits of synthetic biology: The 'telomerator' reshapes synthetic yeast chromosome into more flexible, realistic form, redefining what geneticists can build November 3rd, 2014

Nanoparticles Display Ability to Improve Efficiency of Filters October 28th, 2014

Smallest world record has 'endless possibilities' for bio-nanotechnology October 8th, 2014

Environment

Iranian Experts Clean Uranium-Contaminated Water by Nano-Particles November 23rd, 2014

Silver Nanoparticles Produced in Iran from Forest Plants Extract November 20th, 2014

Nano Sorbents Able to Remove Pollutions Caused by Oil Derivatives November 20th, 2014

Application of Nanocomposites in Production of Photocatalysts for Water Treatment November 17th, 2014

Nanobiotechnology

Quantum mechanical calculations reveal the hidden states of enzyme active sites November 20th, 2014

Tokyo Institute of Technology research: Protein-engineered cages aid studies of cell functions November 19th, 2014

A novel method for identifying the body’s ‘noisiest’ networks November 19th, 2014

Implementation of DNA Chains in Designing Nanospin Pieces November 9th, 2014

Photonics/Optics/Lasers

NRL Scientists Discover Novel Metamaterial Properties within Hexagonal Boron Nitride November 20th, 2014

Penn engineers efficiently 'mix' light at the nanoscale November 17th, 2014

'Direct writing' of diamond patterns from graphite a potential technological leap November 5th, 2014

Outsmarting Thermodynamics in Self-assembly of Nanostructures: Berkeley Lab reports method for symmetry-breaking in feedback-driven self-assembly of optical metamaterials November 4th, 2014

Quantum nanoscience

Quantum mechanical calculations reveal the hidden states of enzyme active sites November 20th, 2014

Pseudospin-driven spin relaxation mechanism in graphene November 11th, 2014

Heat Transfer Sets the Noise Floor for Ultrasensitive Electronics November 11th, 2014

On-demand conductivity for graphene nanoribbons: Physicists from Uzbekistan and Germany have devised a theoretical model to tune the conductivity of graphene zigzag nanoribbons using ultra-short pulses November 10th, 2014

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




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More












ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE