An investigation was made of the electronic relaxation of deep bulk trap and interface states in ZnO ceramics based upon dielectric spectra measured over a wide range of temperature, frequency and bias, in addition to the steady-state response. It considered the nature of net current flowing over the barrier affected by interface state, and then deduced the temperature-dependent barrier height by approximate calculation from steady current-voltage characteristics. Additional conductances and capacitances arising from deep bulk trap relaxation were calculated based upon the displacement of the crossing point between deep bulk trap and Fermi level under a small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies were obtained as 0.22 and 0.35eV; consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation was shown on the dielectric spectra. The DC-like conductance was also observed in high temperature region on dielectric spectra, and the activation energy was much smaller than the barrier height in steady state condition, which was attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.

Electronic Relaxation of Deep Bulk Trap and Interface State in ZnO Ceramics. Y.Yan, S.T.Li, D.Can, P.F.Cheng: Chinese Physics B, 2011, 20[2], 025201