Thermostimulated conductivity and trapping centers in irradiated MgO

Thermostimulated conductivity (TSC) measurements, reinforced on occasion by thermoelectric power measurements, have been made on gamma-irradiated MgO crystals from several sources after a variety of thermal treatments. It has been confirmed that the TSC peak near 90°C is associated with the escape of holes from V− centers. In addition, a persistent electron current extending to below 200°K was observed in relatively high-purity (low-iron) crystals which appears to be associated with shallow electron traps. The free electrons responsible for it are inhibited from recombining with holes in V− centers by Coulomb repulsion. Annealing and air cooling from 1400°C eliminates this electron current and suppresses the over-all amplitude of the thermally stimulated current. The cause of this suppression and the relative insensitivity of the TSC curve to thermal treatment below this temperature are examined on the basis of a simple kinetic model.