Transient photoconductivity in AgCl at room temperature

Abstract

At room temperature silver chloride is an ionic conductor having a relaxation time for polarization of several hundred μsec. A fast-pulse technique is described which makes possible the separation of electronic from ionic currents in this material at 25°C. Primary photoresponse in essential agreement with a simple trapping model is observed. The factors which influence electron lifetimes in pure silver chloride were investigated for crystals containing only a few tenths of a part per million of heavy-metal impurities. A relatively low photoconductive response corresponding to electron lifetimes before trapping of 10 −8 sec or less was found for crystals grown from the melt in vacuum, in a halogen, or in an inert atmosphere. This applies to well-annealed samples and to materials for which precautions were taken to remove water and the products of hydrolysis (Ag and Ag 2O). On the other hand, when crystals are grown in air or from a moist starting charge, electron lifetimes as long as 10 μsec may result. The contribution of holes to fast photoresponse was not observed and must be quite small. For example, in the case of a crystal having a large response at 1000 V/cm field, the ratio of hole range to electron range was found to be < 0.012, yielding an upper limit of hole lifetime of 4 × 10 −9 sec. From measurements with single pulses, the drift mobility of electrons at 26°C is found to be 46±4 cm 2/V sec, in agreement with print-out Hall experiments.