Gallium arsenide x-ray photodiodes for ultrafast physics applications

Semiconductor-based x-ray detectors such as gallium arsenide (GaAs) detectors and silicon detectors have applications in inertial confinement fusion, high-energy-density physics, and synchrotron facility instrumentation. In order to detect rapidly changing signals of interest, scientists are challenged with creating a device that can simultaneously increase hard x-ray absorption while maintaining a response time in the nanosecond scale.

Using GaAs x-ray photodiodes tailored for ultrafast applications, Looker et al. developed a GaAs x-ray detector with a temporal response of just 0.5 ns.

“Fast x-ray detectors allow us to resolve interesting temporal features of the x-ray signals, analogous to creating a camera with a faster shutter time to reduce motion blur,” author Looker said. “Having temporal resolution of a nanosecond can mean the difference between seeing an event of interest or missing it entirely because it’s mixed with the noise.”

Previously, silicon detectors were commonly used because of their availability and mature fabrication processes. The authors demonstrated that GaAs detectors have better hard x-ray absorption with the same detector volume and response time as a silicon detector.

“Our measured resolution of 0.5 ns in this study is exciting, but some experiments require several times faster. Because of some fundamental physical limitations, we likely won’t be able to do better than about 0.1 ns, but we think we can continue to tweak a few things to improve our devices,” said Looker.

The authors theorize that by increasing breakdown voltage on their detector charges might be transported faster, ultimately speeding up the device.

Source: “GaAs x-ray detectors with sub-nanosecond temporal response,” by Quinn Looker, Michael G. Wood, Patrick W. Lake, Jin K. Kim, and Darwin K. Serkland, Review of Scientific Instruments (2019). The article can be accessed at https://doi.org/10.1063/1.5127294 .