Rochester, NY--The National Science Foundation has awarded the Rochester Institute of Technology (RIT) $1.2 million to develop, fabricate, and test a new family of IR detectors grown on silicon wafer substrates by Raytheon Vision Systems. Such detectors could boost IR astronomy and further spur the hunt for exoplanets and the study of the universe’s acceleration. Closer to home, the same technology could also advance remote sensing and medical imaging.
“If this is successful, the astronomy community will have a ready supply of affordable detectors that could be deployed on a wider range of facilities,” says Don Figer, director of the Center for Detectors at RIT and lead scientist on the project. “Right now IR detectors are so expensive that there are only a few on the world’s biggest telescopes—Keck, Gemini, the Very Large Telescope. Those are the only facilities that can afford them, and then they can only afford a few. They have big telescopes with big focal planes and tiny detectors in the middle.”
“The collaboration with RIT leverages over a decade of technological advancements Raytheon has made in manufacturing large format MBE/Si focal planes,” says Elizabeth Corrales, program manager at Raytheon Vision Systems. “Infrared detectors with lower cost focal planes and improved performance will push the boundaries of infrared astronomy and continue Raytheon’s 30-year service to the astronomy community.”
Cost constraints limit the availability and scale of the current detector technology, which use small, expensive cadmium zinc telluride wafers. “Today, a typical state-of-the-art device has 2048 by 2048 pixels at a cost around $350,000 to $500,000,” Figer says. “Detectors on large telescopes can cost a significant fraction of the total instrument budget. Very large, affordable IR arrays will be essential for making optimum use of the proposed 30-m-class ground-based telescopes of the future.”
Up to 196 megapixels
“The key to making larger—up to 14,000 by 14,000 pixels—and less expensive IR detectors lies in using silicon wafer substrates, since large silicon wafers are common in the high-volume semiconductor industry and their coefficient of thermal expansion is well-matched to that of the silicon readout circuits,” Figer says.
For the last 15 years, scientists have pursued the use of silicon substitutes in the quest for large IR detectors. Until now, the crystal lattice mismatch between silicon and IR materials has stymied advancement, causing defects that generate higher dark current, and thus higher noise, reduced quantum efficiency, and increased image persistence. Raytheon has developed the prototype detector technology using a method of depositing light-sensitive material onto silicon substrates while maintaining high vacuum throughout the many steps in the process. The material growth is done using molecular-beam epitaxy.
Figer will also develop a new light-tight detector housing to keep the detector optically and thermally isolated from everything around it. The box-within-a-box design is cooled to 60 K to reduce the blackbody radiation emitted from warmer objects around the detector and prevent additional noise. The National Science Foundation funding to develop the technology will carry Figer and his team to the second phase of the project and the design of a much bigger device on the scale of 4000 by 4000 pixels. An international consortium of organizations is needed to fund the fabrication of these larger detectors.
During the third and final phase of the program, Figer foresees RIT and Raytheon building an instrument for a large telescope. “One of the strategic goals for the Center for Detectors is to start a big astronomical instrumentation program at RIT,” he says. “There are only a handful of programs like that in the world. It’s very competitive but it’s also very fulfilling to both deploy the technology and use it for science in an astronomical instrument.
