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8 August 2018

NASA studies space applications for GaN crystals

© Semiconductor Today Magazine / Juno PublishiPicture: Disco’s DAL7440 KABRA laser saw.

Two teams at the US National Aeronautics and Space Administration (NASA) Goddard Space Flight Center in Greenbelt, MD, USA are being funded to investigate the use of gallium nitride (GaN) to enhance space exploration.

Engineer Jean-Marie Lauenstein and scientist Elizabeth MacDonald are investigating GaN high-electron-mobility transistors (HEMTs) for use in studying how Earth's magnetosphere couples to its ionosphere — a key question in the field of heliophysics which, among other things, studies the forces that drive change in our space environment. Stanley Hunter and Georgia de Nolfo are investigating GaN’s use on a solid-state neutron detector that is relevant to both science and homeland security.

GaN transistors

GaN transistors became available commercially in 2010, but they have not yet found their way into space scientists’ instruments, despite their potential to reduce their size, weight and power consumption. Even though GaN is predicted to be resistant to many types of radiation damage encountered in space, neither NASA nor the US military has established standards characterizing the performance of these transistor-enabled devices when exposed to the extreme radiation in space.

When struck by galactic cosmic rays or other energetic particles, electronic equipment can experience catastrophic or transient single-event upsets. “We have standards for silicon,” says Lauenstein. “We don’t know if the methods for silicon transistors would apply to gallium nitride transistors,” she adds. “With silicon, we can assess the threshold for failure.”

With the funding, Lauenstein and MacDonald are teaming with the Los Alamos National Laboratory in New Mexico, a parts manufacturer, and the NASA Electronic Parts and Packaging to establish criteria assuring that a GaN-type device could withstand the effects of potentially harmful particles produced by galactic cosmic rays and other sources.

The material could be useful in electron-beam accelerators — consisting of GaN transistors — built to map specific magnetic lines in the protective magnetosphere to their footprints in the ionosphere where aurora occur, helping to show how the two regions of near-Earth space connect.

“The team’s research on radiation tolerance helps us understand how to fly these accelerators in the harsh space environment over the mission’s lifetime,” MacDonald says.

According to Lauenstein, these standards will also benefit other scientific disciplines. “We need a path forward for this technology. This opens the door for others to incorporate this technology into their own missions.”

Potentially game changing

For de Nolfo and Hunter, GaN offers a potential solution for building a detector and imaging neutrons, which are short-lived and typically expire after about 15 minutes. Neutrons can be generated by energetic events in the Sun as well as cosmic-ray interactions with the Earth’s upper atmosphere. The neutrons generated by cosmic rays in the atmosphere can add to the Earth’s radiation belt (a swatch of radiation surrounding Earth that, among other things, can interfere with onboard satellite electronics) when they decay. Researchers have discovered that GaN can form the basis of a highly sensitive neutron detector.

In their concept, Hunter and de Nolfo would position a GaN crystal inside an instrument. As neutrons entered the crystal, they scatter off gallium and nitrogen atoms and, in the process, excite other atoms, which then produce a flash of light, revealing the position of the neutron that initiated the reaction. Silicon photomultipliers attached to the crystal convert the flash of light into an electrical pulse to be analyzed by the sensor electronics.

“Gallium nitride is reasonably well understood in the photo-electronics industry, but I think we’re pushing the envelope a little on this application,” says Hunter, adding that the beauty of the concept is that it would contain no moving parts, use little power, and operate in a vacuum. If it works, the instrument would benefit different space science disciplines and the military in detecting nuclear material, he adds.

Tags: GaN HEMT

Visit: www.nasa.gov/centers/goddard

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