PORTLAND, Ore. Russian and U.S. academics are collaborating to develop terahertz silicon germanium chips for "X-ray vision" systems that could peer through suitcases and clothing to identify weapons, through clouds to guide aircraft and through skin to pinpoint cancer. The researchers foresee the chips' use in terahertz scanning spectrometers, just now coming over the technological horizon.
"We are very excited about collaborating with our Russian colleagues. We will combine their work on the theoretical side with our work using SiGe to improve three different types of terahertz emitter chips we have designed," said James Kolodzey, professor of electrical and computer engineering at the University of Delaware (Newark).
Kolodzey's counterpart in Russia is Miron Kagan, director of the Russian Academy's Institute of Radioengineering and Electronics (Moscow). That institute in turn collaborates with the Ioffe Physico-Technical Institute (St. Petersburg).
The terahertz band, centered on 1 THz (1,000 GHz), has been largely neglected because it's too fast for silicon and too slow for optics. But Russian researchers gained extensive experience with the band during a well-funded military project after World War II. Using vacuum tubes, Russian developers turned out complete systems of terahertz emitters and detectors that, despite their heft, define the state of the art in terahertz technology to this day.
Over time, researchers at the Russian Academy of Sciences learned, for example, that terahertz scanners can see inside baggage and that two or more used together enable an absorption spectrogram that can draw on a database of substance signatures to identify the chemical composition of a bag's contents. Terahertz spectrometers use only harmless, nonionizing terahertz-band light.
Kolodzey's lab in Delaware has created three types of terahertz-frequency emitters. Two are based on quantum confinement effects in epitaxially grown quantum wells. The third dispenses with the wells to emit 8-THz photons directly from electrically pumped, boron-doped p-type SiGe at cryogenic temperatures (though the effect is detectable at temperatures as high as 150 Kelvin). "We are very hopeful that one or more of our three designs can be used to create the first solid-state terahertz laser," said Kolodzey.
The scientists predict that the joint work will result in terahertz emitters for applications in biochemical identification, medical diagnostics and cancer research. Funding for the program is provided through the U.S. Civilian Research and Development Foundation.