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Astronomers are always looking to image fainter and farther objects in the night sky. Recent improvements in signal to noise ratio in solid-state detector technology have the potential to provide researchers with the ability to determine photon-number including single photons, allowing them to sense at the limit of physics. The quanta image sensor (QIS), the electron-multiplying charge-coupled device (EMCCD), and the single-photon avalanche diode (SPAD) are three types of next-generation silicon detectors that can capture images with high sensitivity and low input-referred read noise that can result in the ability to count photons. QIS uses a unique CMOS pixel topology that increases conversion gain without impact ionization, reducing readout noise to deep-sub-electron levels and enabling photon-number resolution, high dynamic range, and high spatial resolution. The EMCCD uses a CCD sensor design that amplifies the signal a small amount but very high number of times during readout using impact ionization, reducing readout noise to deep-sub-electron levels and a degree of photon-number resolution. SPAD uses fast in-pixel signal amplification using impact ionization and positive feedback to achieve negligible read noise and is capable of measuring the precise time-of-arrival of photons, enabling high-precision distance measurement and photon-counting. A representative device of each technology was characterized and evaluated with space flight missions in mind. Additionally, a variety of CCD and CMOS image sensors with “Skipper” readout are being explored for photon-number-resolving applications by several groups, including parts of our team, and we will also briefly discuss the Skipper approach in this report. Additionally, recommendations for potential improvements of the technology to better support the astronomical community are made.
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