Evaporation time effects on structural, optical and X-ray photoresponse properties of thermal evaporated a-Se thin films at low vacuum degree

In this work, we prepared the thermal evaporated amorphous selenium (a-Se) thin films with different evaporation time at low vacuum degree 10-2 Pa. The results showed a-Se thin films were easier to be crystallized with prolonging evaporation time. Also, the transmittance absorption edges of a-Se thin films showed a blue shift with the enhanced optical energy gap from 2.08 eV to 2.15 eV. Further, the dark current was found to depend on energy gap, and became lower as extending evaporation time. Moreover, a-Se thin films showed the improved X-ray photocurrent gain, with a rapid photoresponse and a small applied voltage requirement. Overall, this work revealed that the increase of evaporation time led to better deposition quality of thin films, enhancing energy gap and X-ray photoresponse, but thin films were not able to resist to higher temperature anymore.