SINGLE JUNCTIONS IN ZNO VARISTORS STUDIED BY CURRENT-VOLTAGE CHARACTERISTICS AND DEEP-LEVEL TRANSIENT SPECTROSCOPY

The electronic properties of individual grain boundaries in ZnO varist ors were characterized by current-voltage (I-V) measurements and high- temperature zero-bias deep level transient spectroscopy (DLTS). A sing le-junction electrode pattern was designed using photolithography in o rder to study these properties. It was found that interface trap energ y levels and capture cross sections vary with the polarities of trap f illing pulses. The behavior indicates that the grain boundary potentia l barriers are not symmetric. Asymmetry was also observed in I-V measu rements. Intergranular differences in chemical composition, distributi on of chemisorbed oxygen, and grain boundary microstructure were sugge sted to be responsible for the asymmetry in electronic properties.