For the past six years, USD physicists have been working on growing high-grade germanium crystals to be fabricated into germanium detectors. The detectors are used in deep underground experiments, like those at the Sanford Underground Research Facility in the old Homestake Gold Mine in the Black Hills. USD is one of only a handful of places in the world where scientists are growing extremely pure germanium crystals.

"Growing detector-grade germanium crystals, in particular the large-size crystals, is very challenging,” said Dongming Mei, the USD physics professor in charge of growing the crystals. “The greatest challenge is a lack of precise control of individual crystal properties.”

Scientists at USD were able to grow 2.3 kg of high-grade germanium crystal. It was fabricated into a large radiation detector at Texas A&M University. The combination of the crystal’s large size, high purity and good quality set this crystal apart from others. The scientists have produced high-purity germanium crystals before, but this is the first of such a large size. The fabricated germanium detector is now located at the University of Minnesota.

“The new semiconductor crystal growing facility at the University of South Dakota is a unique facility of its kind in an academic setting,” said Vuk Mandic, physics researcher at the University of Minnesota. “Semiconductor detector technology is critical for advancement of high-energy physics and astrophysics, and the USD facility will enable future development and optimization of this technology for different applications.”

USD scientists want to develop an economic way to process large amounts of germanium, both to satisfy the deep underground experiments and to sell commercially. Typically, one-third of each grown germanium crystal produced in the lab is of sufficient purity to allow it to be manufactured into a detector. The remaining fraction of each crystal may be fabricated into wafers that can be used in electro and optical devices and solar panels, with the potential to be sold commercially.

“Germanium crystals have applications across a diverse range of disciplines,” said Tina Keller, director of the USD physics department. “These crystals will have uses in experiments exploring fundamental science topics along with being of interest to industrial partners.”

Download a photo: Physics professor Dongming Mei and one of the germanium crystals grown at USD.

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