Photoconductivity of Silver Chloride Crystals Under Pulsed X-Ray Irradiation

The photoconductivity produced by irradiation with 0.2-μsec 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 μsec) 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×${10}^{-8\mathrm{}}$ ${\mathrm{cm}}^2$/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×${10}^{-9\mathrm{}}$ sec. At higher temperatures the pulses show long tails, and between 200° and 280°K the saturation time varies exponentially with $\frac{1}{T}$. 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 ${\mathrm{Cu}}^{+}$ indicate that the ${\mathrm{Cu}}^{+}$ 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×${10}^{-11\mathrm{}}$ sec, indicating a capture cross section of the Ni ion larger than 300 ${\mathrm{}\left(\mathrm{A}\right)\mathrm{}}^2$.