A Low-Temperature Processed Organic Hole-Blocking Contact Layer for Amorphous Selenium X-Ray Photoconductor

Amorphous selenium (a-Se) X-ray detectors have been used commercially for two decades in mammography because of their high spatial resolution. However, these devices face challenges in high spatial resolution tomography and angiography where lower radiation exposures and dynamic imaging are required. Higher voltages across the selenium layer can potentially improve sensitivity and temporal performance, but dark current is a concern. Although organic polyimide (PI) layers were previously demonstrated to have excellent hole-blocking properties that enabled high voltage mode operation with selenium devices, their higher baking and curing temperatures have restricted usage on the top surface of temperature-sensitive selenium as a hole-blocking layer. In this study, we explore low-temperature SU-8 as a hole-blocking layer for selenium. Our findings reveal that the devices with SU-8 as a hole-blocking layer in either top or bottom configurations maintained a dark current below 1 pA/mm2 even at an increased electric field of 40 V/
$\mu \text{m}$
. Devices with the SU-8 hole-blocking layer at the top surface exhibited a sensitivity loss of 18% after exposure to a cumulative 0.175 Gray (Gy) X-ray while maintaining lag or persistent photoconductivity below 1% at 20 V/
$\mu \text{m}$
. As a comparison, devices fabricated in the same run that utilized the previously reported PI hole-blocking layer at the bottom surface resulted in a sensitivity drop of 24.1% and with lag of ≈3.1%. These results indicate that higher-performance selenium detectors are achievable with SU-8 blocking layers and can expedite the commercial development of low-lag, high-gain selenium X-ray detectors for dynamic medical imaging.