Measurement of photoconductivity of thin amorphous selenium films induced by x-ray radiation

A new x-ray image tube that has two major advantages over existing devices, namely the reduction of x-ray exposure and high resolving power, would be available only if a thin film material of high sensitivity to x-rays and low conductivity under normal conditions can be found. Amorphous selenium was chosen in the first phase to be tested as an x-ray sensitive material. Aluminum-amorphous selenium-aluminum sandwich samples of various thicknesses were evaporated in three consecutive steps. The space-charge -limited current density J was then measured as a function of the voltage V. According to Rose and Lampert, the trapping density and its distribution in energy in an insulator can be deduced from the J-V curves. An exponential trap distribution was obtained experimentally which confirmed the predicted theoretical results. A system of trapping and recombination equations of exponential trap distribution was solved. The rise, decay and steady state changes in conductivity as a function of time under different radiation conditions were calculated and compared with the experimental results. It was found that amorphous selenium is not an ideal target material for our purpose.Electrical and Computer Engineering, Department o