Electrophotographic Charging and Discharging Experiments with Zinc Oxide Single Crystals

Charging experiments have been performed with pure and lithium-doped zinc oxide single crystals under a negatively or positively operating corona. While a negative charging caused a surface voltage of about 45 V with pure zinc oxide crystals and 350 V with Li2O doped crystals, a positive charging supplied surface voltages only of few volts for both types of crystals with a rapid dark-decay. The small difference between the stationary currents during the charging of doped and undoped crystals with the same geometrical surface size and under the same charging conditions was particularly notable. The darkdecay of the doped crystal is much faster than the corresponding decay of the undoped crystal. After a 10 s dark period, however, both crystals exhibited the same surface voltage of about 25 V. The light-decay of the surface voltage of an undoped crystal was comparable to that of zinc oxide-resin layers. The light-decay curves of doped crystals, however were characterized by an unexpected course. During the discharge of these crystals, the surface potential at first became more negative before the expected light discharge occurred.