X-ray Induced Changes in Electronic Properties of Stabilized Amorphous Selenium Based Photoconductors

Amorphous selenium and its alloy are important materials for flat panel digital X-ray detectors. The performance of the X-ray detector is directly related to the carrier mobility and carrier-trapping lifetime of amorphous selenium and its alloy. An experiment was conducted to examine the dose rate effects on the carrier-trapping lifetime reduction of amorphous selenium alloy due to X-ray irradiation. In addition, an experiment was conducted to investigate the temperature effects on X-ray induced carrier-trapping lifetime decrease and relaxation process. X-ray induced capacitance changes have been investigated as well. The interrupted field time of flight (IFTOF) techniques are used in order to acquire the carrier-trapping lifetime. Several amorphous selenium alloy films are irradiated under X-ray. The composition of films are a-Se: 0.3% As: 5ppm Cl and the thickness of the films are about 150 μm. Different dose rates, which range from 0.2 Gy/s up to 2 Gy/s, are applied during the irradiation. The experiments are done for both electrons and holes. The dose rate difference does not result in a significant change in the X-ray induced carrier-trapping lifetime decrease. The same set of samples is studied under three different temperatures, 10 ℃, 23.5 ℃ and 35.5 ℃. The X-ray induced hole-trapping lifetime changes at different temperatures are investigated. After irradiation, the hole-trapping lifetime begins to recovery gradually. The temperature during the relaxation process remains unchanged. The change of hole-trapping lifetime is measured by IFTOF measurement. At higher temperature, upon receiving a certain amount of X-ray dose, the hole-trapping lifetime decreases more than it at lower temperature; however, it also recoveries more quickly at higher temperature. The relaxation process at different temperature also gives activation energy for holes. The X-ray irradiation does not result in any capacitance changes for a-Se films