Radiation Damage in ZnO Single Crystals

Abstract

The radiation and additive coloration of Li-doped and "pure" ZnO crystals have been investigated. The radiation coloration is enhanced by the presence of Li impurity when the radiation temperature is in the range 80-330°K, but the additive coloration is suppressed in Li-doped specimens. The defect production rate, as measured by the increased optical absorption of the samples, is a linear function of electron irradiation intensity and decreases with irradiation energy. The energy dependence of the electron coloration suggests that the defect giving rise to the coloration is produced by the displacement of zinc ions. For a given dose of radiation, fast neutrons (>1 MeV) produce about 30 times as many defects as do energetic electrons. In irradiated crystals the coloration anneals out around 250°C, whereas in additive colored samples the annealing-out temperature is about 900°C. $\gamma$ irradiation during and after annealing indicates that in both cases annealing is complete and not due only to the loss of electrons or holes from the defect center. It is concluded from the study that radiation damage in ZnO occurs primarily as a result of elastic collisions, and that the photochemical processes prevalent in alkali halides contribute very little, if any, to the damage.