This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature,frequency and bias,in addition to the steady state response.It discusses the nature of net current flowing over the barrier affected by interface state,and then obtains temperature-dependent barrier height by approximate calculation from steady I-V (current-voltage) characteristics.Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal.From the resonances due to deep bulk trap relaxation on dielectric spectra,the activation energies are obtained as 0.22 eV and 0.35 eV,which are 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 is shown on the dielectric spectra.The DC-like conductance is also observed in high temperature region on dielectric spectra,and the activation energy is much smaller than the barrier height in steady state condition,which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.
Dielectric relaxation and charge transport induced by electron hopping in ZnO single crystal are measured by using a novocontrol broadband dielectric spectrometer.Typical Debye-like dielectric relaxation originating from electronic hopping between electronic traps and conductive band in surface Schottky barrier region is observed for ZnO single crystal-Au electrode system.However,after insulation of ZnO single crystal by heat treatment in rich oxygen atmosphere,dielectric relaxation and alternating current conductance are observed simultaneously in the dielectric spectra,implying that dielectric relaxation and charge transport can be induced simultaneously by electronic hopping at high temperature in an ordered system.The intrinsic correlation between local dielectric relaxation and long range charge transport offers us a new method to explore complicated dielectrics.
