Electric field and temperature dependence of dielectric permittivity in strontium titanate investigated by a photoemission study on Pt/SrTiO3:Nb junctions

Hirose, Shigeo; Okushi, Hideyo; Ueda, Shigenori; Yoshikawa, Hideki; Adachi, Yutaka; Andõ, Akira; Ohsawa, Takeo; Haneda, Hajime; Ohashi, Naoki

doi:10.1063/1.4921092

Cited by 13 publications

(25 citation statements)

References 19 publications

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“…To quantitatively exploit Fig. 11, the photoemission line was simulated by accounting for the shift with depth due to band bending and the attenuation of photoelectron signal [129][130][131] . The peak intensity reads: where E is the BE, λ is the escape depth of the photoelectron in the ZnO substrate and I(z, E) is the intrinsic line shape of the core level taken as Gaussian herein:…”

Section: B Modeling Of Band Bending Effects On Photoemission Lineshapementioning

confidence: 99%

Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study

et al. 2018

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Band alignment at the interface between evaporated silver films and Zn-or O-terminated polar orientations of ZnO is explored by combining soft and hard X-ray photoemissions on native and hydrogenated surfaces. Ultraviolet Photoemission Spectroscopy (UPS) is used to track variations of work function, band bending, ionization energy and Schottky barrier during silver deposition.The absolute values of band bending and the bulk position of the Fermi level are determined on continuous silver films by HArd X-ray PhotoEmission Spectroscopy (HAXPES) through a dedicated modeling of core levels. Hydrogenation leads to the formation of ∼ 0.3 monolayer of donor-like hydroxyl groups on both ZnO-O and ZnO-Zn surfaces and to the release of metallic zinc on ZnO-Zn. However no transition to an accumulation layer is observed. On bare surfaces, silver adsorption is cationic on ZnO(0001)-O (anionic on ZnO(0001)-Zn) at the earliest stages of growth as expected from polarity healing before adsorbing as a neutral species. UPS and HAXPES data appear quite consistent. The two surfaces undergo rather similar band bendings for all types of preparation. The downward band bending of V bb,ZnO−O = −0.4 eV and V bb,ZnO−Zn = −0.6 eV found for the bare surfaces are reinforced for upon hydrogenation (V bb,ZnO−O+H = −1.1 eV, V bb,ZnO−Zn+H = −1.2 eV). At the interface with Ag, a unique value of band bending of -0.75 eV is observed. While exposure to atomic hydrogen modulates strongly the energetic positions of the surface levels, a similar Schottky barrier of 0.5-0.7 eV is found for thick silver films on the two surfaces.

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Section: B Modeling Of Band Bending Effects On Photoemission Lineshapementioning

confidence: 99%

Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study

et al. 2018

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“…This is of the order of 1–3 nm for standard XPS with laboratory sources (Al Kα: h ν = 1486.6 eV) . At synchrotron sources, photoemission with higher photon energies of up to 10 keV can be performed (HAXPES), leading to mean free paths of up to 10 nm . The deposited film must therefore have a thickness in the low nanometer range.…”

Section: Experimental Approachmentioning

confidence: 99%

Interface Properties of Dielectric Oxides

Klein

2016

J. Am. Ceram. Soc.

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Chemical and electronic properties of dielectric oxide interfaces as obtained using photoelectron spectroscopy are presented and discussed. Interface preparation includes the deposition of metals onto dielectrics and vice versa as well as the effect of postdeposition treatments. Most interfaces are not abrupt as either reduction in the oxide surface occurs during metal deposition or oxidation of the metal substrate is induced by oxide deposition. The Schottky barrier heights at these interfaces are strongly affected by the interface chemistry. Reactive interfaces exhibit a strong Fermi level pinning due to defect formation. Nonreactive interfaces, which are obtained by depositing metallic oxide electrodes, exhibit an unpinned Schottky-Mott-like barrier formation. Barrier heights can therefore be modified by more than 1 eV with suitable electrode material and processing. Postdeposition oxidation and reduction treatments and ferroelectric polarization can lead to comparable changes of barrier height. Interface studies between dielectric oxides reveal the dependence of valence band maximum and conduction band minimum energies. Due to transitivity of band alignment, these can be arranged on an absolute energy scale. The range of Fermi level positions in dielectric oxides, which can also be obtained from photoelectron spectroscopy and which is limited by intrinsic defect formation, is comparable when the oxides aligned on the energy scale determined by the photoemission experiments. The band alignment therefore indicates if a material can be made n-type or p-type by donor or acceptor doping. The range of Fermi levels in the oxides corresponds also with the range of the Fermi levels at oxide/metal interfaces.

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“…The interface between large work function metals (e.g., Au, Pt, Ag…) and n-type Nb-doped SrTiO 3 (NSTO) single crystals attracts great attention for its rich and yet not wellunderstood phenomenology. [1][2][3][4][5][6][7][8][9][10][11][12] In fact, the response of such Schottky contacts turns out to be extremely sensitive to the processing conditions so that largely different transport properties have been reported so far, even for the same nominal system. Specifically, a variety of behaviours spanning from high-quality rectification to hysteretic bipolar resistive switching (RS) are found from room temperature (RT) to $200 K, 1,13 whereas a peculiar polarity reversal progressively dominates the junction response at an even lower temperature.…”

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“…%. 6 Accordingly, the monotonic dependence of / B0 on T reflects a progressive redistribution of the flat-band voltage (V FB $1.6 eV) between the NSTO depletion layer and the interfacial layer, driven by T-induced variations of the depletion width in between $387 nm (at 80 K) and $203 nm (at 290 K). A schematic of such temperature evolution of band bending is shown in Fig.…”

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Temperature- and doping-dependent nanoscale Schottky barrier height at the Au/Nb:SrTiO3 interface

Buzio

Gerbi

Marré

2018

Applied Physics Letters

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We use ballistic electron emission microscopy to investigate prototypical Au/Nb-doped SrTiO 3 (NSTO) Schottky barrier diodes for different temperatures and doping levels. To this end, ultrathin Au overlayers are thermally evaporated onto TiO 2-terminated NSTO single crystal substrates. We show that at room temperature, regardless of the nominal doping, rectification is controlled by a spatially inhomogeneous Schottky barrier height (SBH), which varies on a length scale of tens of nanometers according to a Gaussian distribution with a mean value of 1.29-1.34 eV and the standard deviation in the range of 80-100 meV. At lower temperatures, however, doping effects become relevant. In particular, junctions with a low Nb content of 0.01 and 0.05 wt. % show an $300 meV decrease in the mean SBH from room temperature to 80 K, which can be explained by an electrostatic analysis assuming a temperature-dependent dielectric permittivity for NSTO. In contrast, this model fails to predict the weaker temperature dependence of SBH for junctions based on 0.5 wt. % NSTO. Our nanoscale investigation demands to reassess conventional models for the NSTO polarizability in high-intensity electric fields. Furthermore, it contributes to the comprehension and prediction of transport in metal/SrTiO 3 junctions and devices.

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Electric field and temperature dependence of dielectric permittivity in strontium titanate investigated by a photoemission study on Pt/SrTiO3:Nb junctions

Cited by 13 publications

References 19 publications

Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study

Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study

Interface Properties of Dielectric Oxides

Temperature- and doping-dependent nanoscale Schottky barrier height at the Au/Nb:SrTiO3 interface

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