Direct x-ray detection using thin-film pentacene Schottky diodes

Abstract

Direct x-ray detectors using thermally evaporated pentacene thin-films are fabricated in Schottky and coplanar configurations and are analysed for low x-ray dose rates. In both configurations, the x-ray induced photocurrent is found to be five orders of magnitude greater than the theoretically evaluated threshold value that may reflect possible internal gain mechanism. Coplanar detectors showed unstable x-ray photocurrent characteristics; on the other hand, Schottky photodiode structure showed stable response and thus allowed to proceed for x-ray sensitivity measurements. Pentacene-based Schottky detector presented a decent volume sensitivity of 162.3 μC/mGy/cm3. The high x-ray sensitivity of pentacene Schottky detector can be due to the complete depletion of the thin-film at the operating reverse bias, revealed by transfer characteristics of fabricated pentacene MESFET. Such a reasonably good x-ray photoconversion in low-Z organic semiconducting materials uncovers the possibility of implementing them in x-ray medical dosimetry applications and in wearable electronic technology.