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Description
Low Gain Avalanche Diodes (LGADs) are state-of-the-art silicon sensors designed with an internal gain in the order of 10, enabling a timing resolution of about 30~ps. Over the past decade, the development of LGADs has been driven by the High-Energy Physics (HEP) community to facilitate the time tagging of minimum ionizing particles for the High-Luminosity upgrade of the Large Hadron Collider (HL-LHC). Although LGADs have been extensively studied in HEP due to their fast timing response, their applications in soft X-ray detection remain unexplored.
Detection of soft X-rays with energies in the range of 0.2-2~keV finds application in various topics such as: pharmaceuticals, material science (magnets, superconductors, quantum materials, etc.), and investigating biological samples since it covers K-edges of carbon and oxygen. Key requirements for detecting soft X-rays include high frame rates, a large dynamic range, and a high signal-to-noise ratio. Hybrid silicon pixel detectors can easily meet these requirements, particularly for X-rays with energies ranging from 2 to 10~keV. However, when probing X-rays in the energy range of 0.2-2~keV, hybrid silicon detectors face limitations due to their quantum efficiency and the noise associated with readout electronics.
LGADs with their internal gain mechanism, fast timing capability, high signal-to-noise ratio, and low noise make them an ideal candidate for soft X-ray detection, but with some caveats. This work presents how the LGADs can be designed to detect soft X-rays and an overview of inverse LGADs technology with an optimized entrance window to enhance the quantum efficiency. Different gain design strategies for inverse LGADs and their impact on the spectral response will also be discussed. Furthermore, ongoing and upcoming developments of inverse LGADs and their potential applications in soft X-ray detection will be presented.