Polycrystalline diamond x-ray sensors: intensity and field dependent response

X-ray photoconductive sensors based on high quality polycrystalline diamond were implemented and their response was measured as a function of the incident intensity, at different applied voltage in the range 0-100 V. At each beam intensity, the sensor current increases linearly with applied voltage up to about 50 V, then the increase slows toward a saturation. The sensor responsivity R is independent of the beam intensity Phi only at low applied bias, whereas it decreases according to R~Phi^-1/2 at higher intensities The turning point between these regimes moves at lower radiation intensity for increasing the applied voltage V. Such behavior has been interpreted in terms of different processes dominating the carrier recombination kinetics when the x-ray beam intensity changes over three orders of magnitude.