Photoconductive gain under low-flux X-ray irradiation in 4HCB organic single crystal detectors

A photoconductive gain (up to 400%) is observed in a 4-hydroxycyanobenzene (4HCB, C7H5NO) bulk organic semiconducting detector, resulting in a high sensitivity of 38.8 μC Gyair−1 s−1 cm−2 under 50 kVp X-ray beam irradiation. The gain variation tendency as the function of both the applied bias voltage and the incident X-ray dose rate is revealed. A rising stage at the gain versus dose rate curve is observed at the low-flux range of X-ray irradiation, attributed to the trap-filling process. A deep-trapping dependent model is proposed, in which the hole injection assisted by trapped electrons is responsible for the gain.