Electrical conduction and dielectric breakdown in crystalline NiO and NiO(Li) films

摘要

Charge transport, including dielectic breakdown in NiO films (2minus;10 mgr; thick), is studied as a function of doping (0minus;0.4 at.percnt; Li), temperature (minus;150minus;+150 deg;C), frequency (0minus;108Hz), and voltage using sputtered nickel contact electrodes. The currentIis found to vary asV1at low and asV3at higher fields until a breakdown fieldEsis reached which varies with Li concentrationNasEsprop;Texp(minus;N). The fieldE1at whichIminus;Vnonlinearity begins is given byE1quest;0.2(2kT/eaegr;prime;) andE1prop;Texp(1/T). The ac conductivity sgr; (ohgr;) prop;ohgr;2tgr;2/(1+ohgr;2tgr;2) and the dc conductivity sgr;=sgr;0exp(minus;Eth/kT). These transport properties are shown to be consistent with the hoppingminus;carrier model. Under currentminus;controlled conditions, reversible dielectric breakdown (i.e., repetitive switching) was associated with the fieldminus;induced delocalization of charge carriers. The results are consistent with the view that the charge carriers prior to reversible dielectric breakdown are small polarons.