Temperature Dependence of the Ideality Factor of Ba_1-xK_xBiO₃/Nb-doped SrTiO₃ All-Oxide-Type Schottky Junctions

Current-voltage measurements were performed on Ba_1-xK_xBiO₃/Nb-doped SrTiO₃ (BKBO/STO:Nb) all-oxide-type Schottky junctions in the temperature range of 30 to 300 K. The relative permittivity ε_r(E, T) of undoped SrTiO₃(110) was measured as a function of both temperature and electric field. An anomalous increase in ideality factor n(T) and decrease in zero-bias barrier height Φ_b0(T) with decreasing temperature were observed and were analyzed using the interfacial layer model with a thin insulating interfacial layer present between metal contact (BKBO) and semiconductor interface (STO:Nb). The increase in n(T) at low temperature can be explained by taking into account the temperature dependence of the permittivity of the depletion layer (STO:Nb). The effect of the electric field dependence of the permittivity of STO:Nb on n(T) is also discussed using an approximate electric field dependence, ε_r(T, E)=b/(a+E²)^1/2, where a and b are constants.