Isothermal Capacitance Transient Spectroscopy in ZnO Varistor

Abstract

Isothermal capacitance transient spectroscopy was applied to the ZnO varistor. Spectroscopic signals obtained at around room temperature were related to the interface state of 0.60 eV below the conduction band edge. Furthermore, a bulk trap of 0.27 eV was detected at lower temperatures (121 K∼153 K), which corresponds to the result obtained by admittance spectroscopy.

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

“…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.…”

Deep level transient spectroscopy study of the effect of Mn and Bi doping on trap formation in ZnO

“…The non-linear behaviour is conventionally described in terms of field-dependent current flow across back-to-back double Schottky grain boundary barriers [3,4], which arise due to band-bending by occupied interface states within the bandgap [5]. The breakdown under high electric field is due to the flow of minority carriers, formed by impact ionisation within the depletion region, which lowers the potential barrier [6].…”

“…There is therefore a need for experimental data characterising the depth, density, origin and form of such traps in ZnO varistors, and several experimental studies have addressed this [5,10,13,[17][18][19][20][21][22][23][24][25][26][27][28][29][30] ( Table 1). However the detailed structure and precise role of many of these traps remains unclear.…”

“…Several deep level transient spectroscopy (DLTS) [31] studies have identified electron traps in single crystal ZnO [17][18][19], polycrystalline ZnO [20,21] and ZnO-based varistors [5,10,13,[22][23][24][25][26][27][28][29][30]. DLTS of single crystal semiconductors is normally performed by observing capacitance changes during the emptying of majority carrier traps at deep states in a depletion region that has been created by applying a reverse bias to a surface Schottky contact.…”