P_O2-dependent nonohmic current-voltage characteristics and current-induced redox behavior of junctioned SrTiO₃

Oxide semiconductor junctions formed by attaching p- and n-type SrTiO₃ exhibits a markedly nonohmic current-voltage characteristics at the steady state, showing no typical rectifying characters. Although the voltages which appeared immediately after applying the currents, are completely linear vs. the current values, the probe voltages vary with time and finally result in a significantly nonlinear behavior strongly dependent on oxygen partial pressure, showing distinct asymmetry to the current direction. Separation of the voltage drop into those within the bulks and at the junction reveals that the highly resistive p-type SrTiO₃ bulk near the junction is mainly responsible for the nonohmic character. For the p-type SrTiO₃ single bulk, absorption of oxygen in the gas phase is observed on applying large bias currents, regardless of the current directions. However, the junctioned sample desorbs oxygen for the forward bias, while the reverse bias causes oxygen absorption. Conductivity changes of the highly resistive p-type SrTiO₃ as a consequence of these current-induced redox behavior give a consistent explanation for the direction-dependent nonohmic character of the junctioned sample. Dissociation/association of oxygen due to a shift of the solid-gas equilibrium caused by the applied currents is discussed.