InGaAs/InAlAs Single Photon Avalanche Photodiodes for X-Ray Detection

In this work, we report the performance of InGaAs/InAlAs single photon avalanche photodiodes (SPADs) with different structures for X-ray photon-counting applications. Combined with the high-speed sinusoidally gated quenching technique, InGaAs/InAlAs SPADs with a short dead time and low dark count rate (DCR) achieve a high X-ray photon count rate. A maximum photon count rate of 12 Mcps has been obtained with a 2 GHz repetition frequency at the highest X-ray fluxes. The counting system is close to a non-paralyzable model with a dead time of 56 ns and the linear response count rate is up to 4.1 Mcps (active diameter is
$50 \mu \text{m}$
) at 50 keV, which is suitable for operating in high fluence rates (
$10^{{6}}$
–
$10^{{9}}$
photons/s/mm2) for clinical computed tomography (CT) imaging. Therefore, our results may provide a new approach to improve the performance of X-ray photon-counting detectors (PCDs).