Highly Sensitive InGaAs/InAlAs X-Ray Avalanche Photodiodes With Fast Time Response

Highly sensitive and fast responsive X-ray detectors are crucial for safety, accuracy, and stability in medical diagnosis. To achieve high sensitivity, the thick absorption layer is used to guarantee efficient X-ray photon absorption. However, there is a significant issue that the time response of photodetectors is sacrificed for a thick absorption layer. Herein, we demonstrate the possibility to use InGaAs/InAlAs separate absorption, grading, charge, and multiplication avalanche photodiodes (SAGCM APDs) for highly sensitive X-ray detection with fast time response. Thanks to the internal multiplication, the sensitivity of the optimized device is
$3.1\times 10^{5}\,\,\mu $
CGy−1 cm−2 under 50 keV hard X-ray radiation, which is 14000 times higher than commercial
$\alpha $
-Se detectors. The 3-dB bandwidth of the APDs is 2.93 GHz, corresponding to a time response of 0.34 ns. To overcome the trade-off between sensitivity and time response, we propose a parameter named sensitivity-bandwidth product (SBP) to assess the system performance of the X-ray detector. The device exhibits a higher SBP (
$9.08\times 10^{5}\,\,\mu \text{C}\,\,\cdot $
GHz
$\cdot $
Gy
$^{-1}\,\,\cdot $
cm−2) than any other reported X-ray detector. Our results may provide new strategies to develop a high-performance X-ray detector in medical diagnosis.