Transient behavior in Pt/Nb-doped SrTiO3 Schottky junctions

Abstract

We investigated the transient behavior of Pt/Nb-doped SrTiO3 Schottky junctions that exhibit rectifying and hysteric I-V characteristics. We found that regardless of the junction resistance state, the junction under the bias shows the relaxation behavior over 104 s while the behavior is strongly dependent on the junction resistance state. Detailed investigation of the time dependence of the current and the capacitance of the junctions indicates that the junctions have the inhomogeneous Schottky barrier heights and depletion layer widths while the mean junction profile remains unchanged regardless of the junction resistance state. Given the experimental results, we attribute the observed transient behavior to time-dependent changes in the population of electrons trapped in the local conduction regions under the bias, which play an important role in determining the resistance state of Pt/Nb-doped SrTiO3 junction.

Controlled Current Transport in Pt/Nb:SrTiO3 Junctions via Insertion of Uniform Thin Layers of TaOx

“…The junction capacitances of Pt/TaO x (10 nm)/Nb:STO were significantly reduced compared with those of Pt/Nb:STO junctions (≈210 pF at 0 V compared with ≈450 pF at 0 V), but showed no clear dependence on r O2 for r O2 values of 10–50% (Figure (b)). With regard to the devices’ capacitances, only small differences (≈several percent) were observed between the high resistance state (HRS, after negative voltages) and low resistance state (LRS, after positive voltages), in agreement with previous reports . The capacitance independence of r O2 suggests that the dielectric constants, carrier concentrations, and built‐in potentials (determined form the abscissa intercepts in C −2 – V plots) of the Pt/TaO x /Nb:STO junctions do not have a systematic relationship with r O2 in the r O2 range of 10–50%.…”

“…These phenomena are known to cause “interface‐type” resistive switching, which has been actively investigated for its applications in memory and neuromorphic devices owing to its intrinsic multi‐level/analog switching capability . Pt/Nb‐doped SrTiO 3 (Nb:STO) junctions are known to show clear interfacial resistive switching under reverse bias with relatively high performances . However, the controllability and reproducibility of the resistive switching of Pt/Nb:STO is poor because they are highly sensitive to fabrication conditions .…”

“…The ϕ B values show a clear dependence on r O2 in the 10–50% region (Figure (c)), whereas the C – V measurements suggest that the built‐in potentials are independent of r O2 in this range. The deviation between the values of ϕ B determined from the I – V and C – V characteristics is typical of Pt/Nb:STO junctions and has been attributed to the formation of local low‐resistance regions at the junction interfaces . From this perspective, the C – V characteristics (Figure (b)) can be treated as the areal sums of the overall junction capacitances, while the I – V characteristics (Figure ) can be treated as predominantly caused by large current flows in local regions with lower ϕ B .…”

Resistive switching and its suppression in Pt/Nb:SrTiO3 junctions

“…The increase in n and the lowering of φ B on switching the junction to the LRS are generally observed for this type of resistive switching memory. It has been ascribed to barrier inhomogeneity811181920, because the global φ B as measured in photocurrent experiments is insensitive to resistive switching1921.…”

“…One extensively studied type of resistive switching device consists of a Schottky junction between a doped, wide-band gap oxide, such as SrTiO 3 , and high work-function metals such as Pt, Au or metallic oxides such as SrRuO 3 and YBa 2 Cu 3 O 7− x 6789. In such devices, resistive switching is accompanied by a modulation of the effective Schottky barrier height78101112. These devices combine technologically attractive features, such as hysteretic current–voltage ( I – V ) characteristics with large on/off ratios, bipolar switching and continuously tunable resistance states.…”