New structure could produce efficient semiconductor laser sources

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.

“The novel structure will produce lasers with more power and that are more efficient, reliable and stable,” says Dan Botez, Electrical and Computer Engineering Philip Dunham Reed Professor. He 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, current mid-infrared laser technologies for detecting explosives 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. Called metalorganic chemical vapor deposition (MOCVD), the process involves exposing a substrate to high heat and chemicals, causing the formation of layers on the substrate in an atomic-lattice configuration. Unlike previous crystal growth techniques, MOCVD allows manufacturers in addition to laboratory scientists to fabricate laser structures with varying compositions.

Varying the layers’ composition is important in building a structure that prevents electrons from escaping the laser structure, a process called carrier leakage. “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.

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

For a more detailed story about the structure Botez and Mawst have created, visit http://www.engr.wisc.edu/news/headlines/2009/Dec07.html.