Electrical properties and electroluminescence of ZnO composite thin-film varistors

ZnO composite thin films (ZnO-Bi/sub 2/O/sub 3/ two-layer thin films) were prepared by RF and ion-beam sputtering. The reverse-biased ZnO composite two-layer films showed highly nonlinear conduction, and its mechanism is discussed on the basis of current-voltage, capacitance-voltage, and electroluminescence characteristics. The bandgap electroluminescence (3.2 eV) from the ZnO-Bi/sub 2/O/sub 3/ two-layer sample was observed in the breakdown region. This suggests that holes are generated in the ZnO depletion layer and modify the interfacial barrier height in the breakdown region. The capacitance of the ZnO-Bi/sub 2/O/sub 3/ two-layer sample decreased steeply in the breakdown region. This is associated with barrier height modulation by trapping of minority carriers at the grain boundary and supports the above explanation.<
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