{"71170":{"#nid":"71170","#data":{"type":"news","title":"Avalanche Photodiodes Target Bioterrorism Agents","body":[{"value":"\u003Cp\u003EResearchers have shown that a new class of ultraviolet photodiode could help meet the U.S. military\u0027s pressing requirement for compact, reliable and cost-effective sensors to detect anthrax and other bioterrorism agents in the air.\u003C\/p\u003E\n\u003Cp\u003E\u0022The 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,\u0022 said Russell Dupuis, Steve W. Chaddick Endowed Chair in Electro-Optics in Georgia Tech\u0027s School of Electrical and Computer Engineering (ECE) and a Georgia Research Alliance Eminent Scholar.\n\u003C\/p\u003E\n\u003Cp\u003ENew 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 \u003Cem\u003EElectronics Letters\u003C\/em\u003E and the November 2007 issue of the journal \u003Cem\u003EIEEE Photonics Technology Letters\u003C\/em\u003E.\n\u003C\/p\u003E\n\u003Cp\u003EECE 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. \n\u003C\/p\u003E\n\u003Cp\u003EThe 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 emit ultraviolet light, the researchers designed special photodiodes that detect the fluorescence in the ultraviolet region, but have no response to visible light.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022We built our photodiodes with gallium nitride, which is a semiconductor that can be used to create photodiodes that require no filters because this material has an inherent response to ultraviolet, but no response to visible light,\u0022 explained Dupuis.\n\u003C\/p\u003E\n\u003Cp\u003ETo improve the sensitivity at ultraviolet wavelengths, the researchers designed the gallium nitride photodiodes to operate in a mode that employs avalanche multiplication. The avalanche multiplication phenomenon is used to multiply normally tiny currents by factors of up to one million, thus dramatically increasing the device gain.\n\u003C\/p\u003E\n\u003Cp\u003EAvalanche photodiodes can create much larger currents for each photon compared to normal photodiodes. Once the necessary electric field strength has been achieved inside the device, the avalanche effect starts with just one free electron. Since the illuminated photodiode will contain many free electrons, an avalanche will always occur if the electric field is large enough.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022One electron-hole pair that is produced by a photon absorption event creates a million other electron-hole pairs and the current becomes a pulse of current that you can detect with special electronics,\u0022 added Dupuis. \n\u003C\/p\u003E\n\u003Cp\u003EThe researchers fabricated high-performance gallium nitride ultraviolet avalanche photodiodes on bulk gallium nitride substrates that demonstrate optical gains of 100,000 at ultraviolet wavelengths from 280 to 360 nanometers. \n\u003C\/p\u003E\n\u003Cp\u003EThe gallium nitride device structures were grown by metalorganic chemical vapor deposition, a technique for depositing thin layers of atoms onto a semiconductor wafer. Many layers can be built up, each of a precisely controlled thickness and composition, to create a material which has specific optical and electrical properties. This is the first time gallium nitride was successfully used in the fabrication of photodiodes having ultraviolet optical gains greater than 10,000.\n\u003C\/p\u003E\n\u003Cp\u003ESince demonstrating the feasibility of the photodiodes to exhibit the avalanche effect, the research team has been developing a more advanced structure capable of operating as a Geiger-mode detector, so that the photodiodes are sensitive enough to detect only one photon at a time. When the Geiger-mode detector is connected to the avalanche circuitry, a single electron-hole pair can trigger a strong avalanche current to flow from just one photon.\u003C\/p\u003E\n\u003Cp\u003EYoder, who works at Georgia Tech\u0027s Savannah, Ga. campus, is developing computer models of the new photodiodes to calculate the detailed electronic and optical transport. Yoder\u0027s goal is to optimize the materials and design of the Geiger-mode avalanche detector to assure optimal, reproducible performance of the avalanche photodiodes.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022Doug\u0027s work is pivotal because these applications don\u0027t require one working detector, they might require thousands of uniform detectors in the same chip that all function the same way, so our ability to manufacture identical photodiodes and detectors is important,\u0022 said Dupuis.\n\u003C\/p\u003E\n\u003Cp\u003EWith proper manufacturing, these avalanche photodiodes can be used for more than detecting bioterrorism agents. They can also be used detect fires, gun muzzle flashes, missile propulsion flames and maybe even cancer cells, according to Dupuis.\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cem\u003EThe DARPA funding was supported by the Deep Ultraviolet Avalanche Photodetectors (DUVAP) program contract FA8718-07-C-0002.\u003C\/em\u003E\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 100\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\n\u003C\/strong\u003E\u003C\/p\u003E\n\u003Cp\u003EMedia Relations Contacts: Abby Vogel (404-385-3364); E-mail: (\u003Ca href=\u0022mailto:avogel@gatech.edu\u0022\u003Eavogel@gatech.edu\u003C\/a\u003E) or John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter:\u003C\/strong\u003E Abby Vogel\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"Ultraviolet photodiodes demonstrate high optical gains"}],"field_summary":[{"value":"Researchers have shown that a new class of ultraviolet photodiode could help meet the U.S. military\u0027s pressing requirement for compact, reliable and cost-effective sensors to detect anthrax and other bioterrorism agents in the air.","format":"limited_html"}],"field_summary_sentence":[{"value":"New class of ultraviolet photodiodes developed"}],"uid":"27206","created_gmt":"2008-06-25 00:00:00","changed_gmt":"2016-10-08 03:03:19","author":"Abby Vogel Robinson","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2008-06-25T00:00:00-04:00","iso_date":"2008-06-25T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"71171":{"id":"71171","type":"image","title":"Russell Dupuis","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894630","gmt_changed":"2016-10-08 02:43:50"},"71172":{"id":"71172","type":"image","title":"Avalanche photodiodes","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894630","gmt_changed":"2016-10-08 02:43:50"},"71173":{"id":"71173","type":"image","title":"Russell Dupuis photodiode","body":null,"created":"1449177348","gmt_created":"2015-12-03 21:15:48","changed":"1475894630","gmt_changed":"2016-10-08 02:43:50"}},"media_ids":["71171","71172","71173"],"related_links":[{"url":"http:\/\/dx.doi.org\/10.1049\/el:20082830","title":"Electronics Letters article"},{"url":"http:\/\/www.ece.gatech.edu\/faculty-staff\/fac_profiles\/bio.php?id=105","title":"Douglas Yoder"},{"url":"http:\/\/www.ece.gatech.edu\/faculty-staff\/fac_profiles\/bio.php?id=134","title":"Shyh-Chiang Shen"},{"url":"http:\/\/www.ece.gatech.edu\/faculty-staff\/fac_profiles\/bio.php?id=129","title":"Dr. Russell Dupuis"},{"url":"http:\/\/dx.doi.org\/10.1109\/LPT.2007.906052","title":"IEEE Photonics Technology Letters"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"145","name":"Engineering"},{"id":"147","name":"Military Technology"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"1132","name":"anthrax"},{"id":"7327","name":"avalanche"},{"id":"1364","name":"chemical"},{"id":"7339","name":"deposition"},{"id":"6884","name":"electron"},{"id":"6891","name":"fluorescence"},{"id":"7331","name":"gain"},{"id":"7332","name":"gallium"},{"id":"7340","name":"Geiger"},{"id":"7336","name":"hole"},{"id":"7337","name":"metalorganic"},{"id":"7334","name":"multiplication"},{"id":"7333","name":"nitride"},{"id":"7330","name":"optic"},{"id":"7335","name":"phenomenon"},{"id":"7328","name":"photodiode"},{"id":"3136","name":"photon"},{"id":"167609","name":"semiconductor"},{"id":"167318","name":"sensor"},{"id":"997","name":"terrorism"},{"id":"7329","name":"ultraviolet"},{"id":"7338","name":"vapor"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003EAbby Robinson\u003C\/strong\u003E\u003Cbr \/\u003EResearch News and Publications\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=avogel6\u0022\u003EContact Abby Robinson\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-385-3364\u003C\/strong\u003E","format":"limited_html"}],"email":["abby@innovate.gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}