Performance Evaluation of an Amorphous Selenium Photodetector at High Fields for Application Integration

Polyimide (PI) has been utilized as a hole-blocking layer (HBL) in high-resistivity photoconductors such as amorphous selenium (a-Se) and amorphous lead oxide (a-PbO). It prevents hole injection from the positively biased electrode and suppresses the dark current of the detector. To determine the performance parameters of an a-Se/PI detector for readout design and specification for different radiation detection applications, knowledge of the accurate voltage drop within the photoconductor is crucial. Here, we precisely determine the voltage drop across a-Se when interfaced with a thin layer of PI ( $1 \mu \text{m}$ ) and characterize its temporal resolution (rise time and jitter), dynamic range, and quantum efficiency (QE) as a function of the electric field. The photoresponse of the detector is characterized using light-emitting diodes in the ultraviolet (UV, 355–400-nm wavelength) and visible (400–533-nm wavelength) regions of the light spectrum. We find the voltage drop across a-Se as 91% of the total applied voltage. This results in a QE near unity at 405 nm for corrected fields beginning at 45 V/ $\mu \text{m}$ . At fields of 50 V/ $\mu \text{m}$ , we observe rise times of 3.7 ns and jitter of 130 ps.