Avalanche photodiodes target bioterror...( Researchers have shown that a new cl...)

Researchers have shown that a new class of ultraviolet photodiode could help meet the U.S. military's pressing requirement for compact, reliable and cost-effective sensors to detect anthrax and other bioterrorism agents in the air.

"The military is currently using photomultiplier tubes, which are bulky, fragile and require a lot of power to run them, or silicon photodiodes that require a complex filter so that they only detect the desired ultraviolet light," said Russell Dupuis, Steve W. Chaddick Endowed Chair in Electro-Optics in Georgia Tech's School of Electrical and Computer Engineering (ECE) and a Georgia Research Alliance Eminent Scholar.

New research shows that ultraviolet avalanche photodiodes offer the high gain, reliability and robustness needed to detect these agents and help authorities rapidly contain an incident like the 2001 anthrax attacks. The fabrication methods and device characteristics were described at the 50th Electronic Materials Conference in Santa Barbara on June 25. Details of the photodiodes were also published in the February 14 issue of the journal Electronics Letters and the November 2007 issue of the journal IEEE Photonics Technology Letters.

ECE associate professor Douglas Yoder, assistant professor Shyh-Chiang Shen and senior research engineer Jae-Hyun Ryou collaborated on this research, which is funded by the Defense Advanced Research Projects Agency (DARPA) and the Georgia Research Alliance.

The team chose to develop avalanche photodiodes for this bioterrorism application because the devices can detect the signature fluorescence of biological molecules in a sample of air. Since most of the molecules of interest to the researchers emit ultraviolet light, they designed special photodiodes that detect the fluorescence in the ultraviolet region, but have no response to visible light.

"We built our photodiodes with gallium nitride, which is a semiconductor that can
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