Characterization of the Interface States in ZnO Varistors by DLTS Method

First-Principles Calculations of Co Impurities and Native Defects in ZnO

“…As an origin, excessive oxygen at the interfaces has been suggested. 7,13) This is consistent with experimental reports that nonlinear characteristics strongly depend on oxygen partial pressure during heat treatment and sintering processes, 14,15) and that oxygen accumulation is more abundant at intergranular-fractured surfaces in untreated samples than in electrically degraded samples. 16,17) The excessive oxygen at interface regions may be regarded as segregation of native defects associated with oxygen excess such as Zn vacancies and O interstitials.…”

“…18,21,22) Regarding the energies of electronic states, the unoccupied parts of interfacial states have been experimentally observed at 0.6-1.0 eV below the conduction band minimum. [6][7][8][9][10][11] Considering an experimental band gap of 3.30 eV, these should correspond to 2.3-2.7 eV above the valence band maximum. In the present results, the acceptor-type states associated with Zn vacancies are located close to the valence band maximum.…”

“…[1][2][3] The nonlinearity is attributed to the double Schottky barriers that originate from the formation of acceptor-type states at the interfaces between donor-rich grains. 4,5) Although the interfacial electronic states have been intensively investigated because of the importance in the nonlinear behavior, [6][7][8][9][10][11][12][13] the explicit origin still remains open. As an origin, excessive oxygen at the interfaces has been suggested.…”

Synthesis and Characterization of ZnO/Glass/ZnO Structures Showing Highly Nonlinear Current-Voltage Characteristics

“…[29][30][31][32][33][34][35] Moreover, the value of E c À E t evaluated for P3 (0.95 eV) was very close to that reported for ZnO ceramic varistors. 22) The electronic structure in the glass/ZnO interface region can thus be concluded to be similar to that at the active grain boundaries in ordinary ZnO ceramic varistors.…”

“…The AC signal applied for C-V measurements was 1 MHz and 10 mV. To analyze the energy diagram of the trap states, transient capacitance (C-t) measurements were also carried out using a DL8000 DLTS system (Accent Optical Technologies Inc., Bend, OR) with an AC signal amplitude set to 0.1 V. The temperature range for the C-t measurements was 80-350 K. The results of the C-t measurements were converted to deep level transient spectra [28][29][30] (DLTS) to evaluate the energy dispersion of the trap states. Figure 1 shows the XRD patterns for BBCMO and BnCMO (see Table 1) after quenching from the molten state.…”