Orientation and Temperature Dependence of the Photoplastic Effect in ZnO

Abstract

The photoplastic effect in ZnO is observed as a strong reversible increase in flow stress, during illumination with white light, when single crystals are deformed in basal slip at room temperature. An earlier model based on Read's theory for the space-charge region near a charged dislocation has been confirmed by further measurements. Basal dislocations in the wurtzite lattice are expected to show different electrical behavior than prismatic dislocations. The basal dislocations contain atoms of the same kind in the dislocation line and are expected to be electrically active through electron trapping to dangling bonds. The prismatic dislocations have alternating kinds of atoms in the dislocation line and are expected to be electrically inactive by a possible interlock of the broken bonds. Therefore, dislocations in prismatic slip should be uncharged and show no photoplastic effect. This was confirmed by experiments showing that there is no observable effect of illumination on the flow properties when crystals are deformed in prismatic slip. The different electrical activity of the dislocations in the two slip systems is also reflected in the resistivity and photoconductivity behavior of deformed samples.