Investigation of Temperature-Dependent Hard X-ray Photoemission Spectra on Au/Nb:SrTiO₃ Schottky Junctions

Abstract

With the temperature and electric field dependence of the dielectric permittivity of Schottky junctions, conventional methods cannot fully capture the properties of the junctions. Hard X-ray photoemission spectroscopy (HAXPES) has been used in characterizing device stack structures. In this study, HAXPES was employed to investigate the temperature dependence of the electronic band structures at Schottky junctions composed of Au and niobium-doped n-type strontium titanate (Nb:SrTiO3). The Au/Nb:SrTiO3 Schottky junctions were formed by magnetron sputtering. HAXPES revealed the band-bending profiles at the junctions. The core-level spectra of the buried Nb:SrTiO3 showed peak broadening and a shift, indicating the formation of a potential barrier at the interfaces. The temperature dependence of these spectral features, along with the hysteresis loops observed in the current–voltage characteristics, changed significantly as temperature decreased, indicating the reduction of the Schottky barrier width with decreasing temperature. The simulated HAXPES profiles deduced from the calculated potential distribution were consistent with the observed HAXPES profiles. However, comparison of both temperature-dependent HAXPES profiles indicates the conventional phenomenological model is not completely appropriate and the importance to reassess it for the dielectric permittivity of Nb:SrTiO3 at low temperatures under a high electric field.

Protons: Critical Species for Resistive Switching in Interface‐Type Memristors

“…This forming‐free bipolar switching behavior in our devices matches well with the previous reports in M/Nb:STO devices. [ 39,43 ] Also, our results indicate that M/Nb:STO devices show an interface‐type resistive switching rather than filament‐type. The overall voltage sweeping sequence of 0 → 3 → −6 → 0 V shows large hysteresis loop with a high on/off ratio (>10 4 at 0.6 V) as displayed in Figure 1e, which is important for applications.…”

“…Reduction in I – V hysteresis at increased temperatures has been reported for M/Nb:STO junctions and correlated to thermally activated processes like tunneling, thermionic emission and thermionic‐field emission. [ 33,38,43 ] In addition, local heating induced small‐scale inhomogeneity of the Φ B , and redistribution of interface deep level traps could be accountable for this effect as reported. [ 42,49 ]…”

“…Ohsawa and co‐workers reported that I – V hysteresis was not observed in as‐prepared Au/Nb:STO and the rectifying properties emerge after exposing the devices to air. [ 43 ] We have observed that the I – V hysteresis and shape can change with measurements (Figure 2) and weather (data not shown). In fact, in FT memristor, moisture can induce a large variation in I – V and C – V measurements.…”

“…This is consistent with the developed strong Schottky barrier due to trapped charge species at the interface. [42,43] Next, we examined the bias voltagedependent RS of our device as shown in Figure S2(c),(d) (Supporting Information). With varying SET voltages between 0.5 and 3 V and fixed RESET voltage at −6 V, the HRS remains the same, while LRS current gradually increases.…”

Resistive switching suppression in metal/Nb:SrTiO3 Schottky contacts prepared by room-temperature pulsed laser deposition

“…charge trapping/detrapping at oxygen-vacancy-induced defect states localized at the interfacial layer) [15,16,[18][19][20][21], several studies invoke field-assisted oxygen-ions migration and interfacial redox reactions [17,22,23]. Importantly, switching devices are often found to interact with the environment, as both ambient oxygen and moisture may modulate ϕ B and RS by promoting (or preventing) the excorporation/incorporation of ionic species within the interfacial layer [17,21,[24][25][26][27]. Given the complex nature of the NSTO interfacial layer and of the RS mechanisms, attempts to improve reproducibility and uniformity of electronic transport across M/NSTO SBDs have moved along different directions including in situ NSTO surface cleaning [1,2,28], post-growth thermal treatments [14,29,30], insertion of oxide interlayers [17,19,30], modulation of ambient gases [21,24], and tailored growth of epitaxial electrodes [19].…”