Effects of dopants on the deep bulk levels in the ZnO-Bi2O3-MnO2 system

Small amounts of In2O3 and Li2O were added to the ZnO-Bi2O3-MnO2 ternary primitive varistor system. Considering Schottky disorder and Frenkel disorder, oxygen vacancy or zinc interstitial density was expected to decrease with In2O3 doping and to increase with Li2O doping. Using admittance spectroscopy, a 0.32-eV electron trap, which is suggested to be an ionized oxygen vacancy, was observed regardless of the doping conditions. Changes in the peak height, for the 0.32-eV trap, in the admittance spectra are correlated with In2O3 and Li2O doping. Doping with In2O3 reduces the conductance contribution due to the trap, while doping with Li2O enhances it. However, calculations show that small amounts of dopants, less than 100 ppm, do not greatly influence the trap density. The trap density remains within experimental error approximately 1.0×1017 cm−3.