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Harvard team takes major step toward high volume production of quantum cascade lasers

Breakthrough could soon lead to the large-scale commercialization of QC lasers and open up new markets for laser based chemical sensors

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Michael Rutter
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Cambridge, Mass. - May 15, 2006 -Applied scientists from Harvard University have, for the first time,demonstrated high-power continuous wave (cw) room temperature quantum cascade (QC) lasers made by a well-established mass production semiconductor synthesis technique. The breakthrough could soon lead to the large-scale commercialization of QC lasers and open up new markets for laser based chemical sensors.

The new generation of QC lasers relies on a layer deposition technique known as Metallorganic Vapor Phase Epitaxy (MOVPE), one of the most common and versatile methods for mass-producing technology for semiconductor lasers, circuits and other photonics components for communications.

"By pulling together complementary strengths in the quantum design of QC lasers and in MOVPE technology, the team has achieved record performance that will enable a wide range of commercial and military applications," said Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard's Division of Engineering and Applied Sciences.

Quantum cascade lasers were invented and first demonstrated by Capasso and his group at Bell Labs in 1994. These powerful and portable lasers are made by stacking ultra-thin atomic layers of semiconductor materials on top of each other, traditionally using a growth technique called Molecular Beam Epitaxy (MBE). By varying the thickness of the layers scientists can select the wavelength at which a QC laser will emit light, custom designing it for a specific application. The range of applications of QC laser based chemical sensors is very broad, including pollution monitoring, medical diagnostics such as breath analysis, and applications for homeland security.

"Compared with MBE, which was until recently the preferred growth technique for QC lasers, the MOVPE method allows the deposition of uniform and thick layers at high growth rates," said Capasso. "The technique also offers excellent stability and shorter machine downtime, ideal characteristics for industrial production. Moreover, the reduced cost for this technology will ultimately decrease the cost of future QC lasers."

The team demonstrated MOVPE-based QC lasers operating at wavelengths near five and eight microns, two spectral regions of paramount importance in chemical detection. The lasers emitted cw power levels in excess of 200 mW at room temperature and operated in continuous mode at temperatures as high as ~130 degrees Celsius (266 degrees Fahrenheit). Further, the researchers performed reliability tests that indicated a remarkable degree of robustness for the lasers. Measured at room temperature conditions, the laser characteristics did not degrade after more than 500 hours of cw operation at 100 degrees Celsius - the equivalent of running the device for approximately eight consecutive years at room temperature.

"The demonstration paves the way for practical applications of QC lasers," says Gloria Höfler, who led the team from Agilent Technologies(1) that participated in this research during 2004-2005 and contributed to the realization of the devices and the method of growth.

Published in the May 15th issue of Applied Physics Letters, Capasso's coauthors are Laurent Diehl, Mariano Troccoli and Marko Loncar from Harvard's Division of Engineering and Applied Sciences, and scientists who conducted research at Agilent Technologies' corporate research laboratories - Gloria Höfler, David Bour, Scott Corzine and Jintian Zhu.

The research was sponsored with financial support from Agilent Technologies, the U.S. Army Research Laboratory and the U.S. Army Research Office, and from DARPA (Optofluidics center). The authors also acknowledge the support of the Center for Nanoscale Systems (CNS) at Harvard University.

(1) Agilent Technologies sold its semiconductor business to Kohlberg Kravis Roberts & Co. and Silver Lake Partners in December 2005. The business is now a separate company, called Avago Technologies.