Abstract
Dielectrics has attracted wide attention as its potential application in high-density energy storage system, electronic devices’ miniaturization such as field effect transistors. An acceptor-donor method is attempted in our work to design the defect complex, where the electron in confined. In our study, the (Lix, Aly)Zn1-x-yO ceramics were fabricated via solid state sintering process. When x=0.33%, y=0.67%, the dielectric property was optimized showing a relatively good frequency stability with e=9862, tand=0.16 at 1 kHz. The impedance spectroscopic analysis shows the nonexistence of the resistive grain boundaries and semiconducting grain, which indicates that the traditional internal barrier hopping capacitance mechanism is not the origin leading to the observed colossal dielectric constant phenomenon. Moreover, two relaxation P1 and P2 were identified by the Modulus spectroscopy. Further analysis including the annealing process and luminescence spectroscopy shows that P1 relaxation process may originate from O-poor defect such as oxygen vacancies, and the O-poor defects mainly aggregate at grain boundaries and also the surface layer. For both the as grown and oxygen annealed samples, the ac conductivity obeys the correlated barrier hopping mechanism. Combined the correlated barrier hopping model and Kirkwood’s polarization theory, the dielectric constant and frequency dependent dielectric constant were stimulated. It shows that the relaxation P1 and P2 would both contribute to the dielectric constant (~10016) and loss (0.149) while only P2 would contribute to the dielectric constant (~2699) and loss (0.05). Meanwhile, P2 is related with the LiZn-AlZn related defect dipoles. The (Ga, Cu) co-doped ZnO thin films were fabricated by Pulse Laser Deposition method. When the dopant ratio of Ga and Cu are 0.5 wt% and 8 wt%, and P(O2) = 5 Pa, the dielectric property was optimized exhibiting a relatively good frequency stability, and the dielectric constant and loss are 204 and 0.27 at 1 kHz. In the dielectric spectroscopy, one Lorentzian peak was identified and attributed to the oscillator’s resonance. Simulation results shows that the resonance process is uncapable of producing the large dielectric constant. One relaxation process P1 was identified in the Modulus spectroscopy and related to the Correlated barrier hopping process. The simulation reveals that the relaxation P1 would contribute to the dielectric constant of 204 and loss of 1.12, and the calculated ε(ω) exhibits relatively good frequency stability as same as the experimental data. The band offset between (Ga, Cu) co-doped ZnO and p-type Silicon was investigated using XPS measurement. It is found that a 1.47 nm layer of SiO2 exists at the interface, and the conduction and valence band offset are 0.17 and 2.42 eV respectively.
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