Photoconductivity of Silver Chloride Crystals Under Pulsed X-Ray Irradiation

The photoconductivity produced by irradiation with 0.2-{μ}sec x-ray pulses was studied in AgCl as a function of temperature (80-280^∘{}K), x-ray intensity and penetration, field strength, and crystal preparation, in order to obtain information about lifetimes and mobilities of electrons and holes. The measurements of electron lifetimes ({~}1 {μ}sec) and mobilities in air-grown crystals are in agreement with those reported in the literature. The photoconductive response can be described by assuming deep electron traps throughout the volume of the crystal and possibly a disturbed surface layer. No hole motion is observed below 250^∘{}K; above that temperature the schubweg per unit field is estimated at 5×{}10^-8 cm²/v. The electron lifetime in crystals grown and annealed in He is much smaller than in the air-grown samples. Assuming the same mobility in both samples the life-time at 80^∘{}K is 3×{}10^-9 sec. At higher temperatures the pulses show long tails, and between 200^∘{} and 280^∘{}K the saturation time varies exponentially with 1/T. It is assumed that shallow traps exist ({~}0.08 ev) in a thin surface region which otherwise has a long electron lifetime as compared with the bulk of the crystal. Measurements on crystals doped with 20 ppm Cu⁺ indicate that the Cu⁺ ions do not act as effective electron traps. On the other hand, the presence of 1 ppm Ni ions reduces the lifetime at 80^∘{}K to less than 3×{}10^-11 sec, indicating a capture cross section of the Ni ion larger than 300 (A)².