Spectroscopic evidence of in-gap states at the SrTiO3/LaAlO3 ultrathin interfaces

Drera, Giovanni; Banfi, Francesco; Canova, F. Federici; Borghetti, Patrizia; Sangaletti, L.; Bondino, Federica; Magnano, Elena; Huijben, J.; Huijben, Mark; Rijnders, Guus; Blank, D. H. A.; Hilgenkamp, H.; Brinkman, Alexander

doi:10.1063/1.3549177

Cited by 55 publications

(61 citation statements)

References 20 publications

(23 reference statements)

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“…3 shows estimates of the ground state electron level associated to the double donor state arising at the interface due to an O vacancy at the surface. These trapped interface levels may be the 'in-gap states' seen in a recent spectroscopic study 30 . For a thin film the traps are deep and few, but as it grows thicker, the donor states become shallower and the area density of traps grows, as illustrated in the inset of Fig.…”

Section: Onset Of Conduction: Electron Trappingmentioning

confidence: 99%

Surface defects and conduction in polar oxide heterostructures

2011

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The polar interface between LaAlO3 and SrTiO3 has shown promise as a field effect transistor, with reduced (nanoscale) feature sizes and potentially added functionality over conventional semiconductor systems. However, the mobility of the interfacial two-dimensional electron gas (2DEG) is lower than desirable. Therefore to progress, the highly debated origin of the 2DEG must be understood. Here we present a case for surface redox reactions as the origin of the 2DEG, in particular surface O vacancies, using a model supported by first principles calculations that describes the redox formation. In agreement with recent spectroscopic and transport measurements, we predict a stabilization of such redox processes (and hence Ti 3d occupation) with film thickness beyond a critical value, which can be smaller than the critical thickness for 2D electronic conduction, since the surface defects generate trapping potentials that will affect the interface electron mobility. Several other recent experimental results, such as lack of core level broadening and shifts, find natural explanation. Pristine systems will likely require changed growth conditions or modified materials with a higher vacancy free energy.

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Section: Onset Of Conduction: Electron Trappingmentioning

confidence: 99%

Surface defects and conduction in polar oxide heterostructures

2011

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“…Photoemission spectroscopy of buried interfaces is more challenging due to the small inelastic electron mean free path in solids, which, over a wide range of photon energies (hν), is of the order of 1 nm. However, it was shown recently that a combination of soft x-ray photoemission with resonant photoexcitation [14][15][16][17][18] can overcome this limitation. By selecting hν at the Ti L edge, the signal of the Fermi states associated with conducting electrons is greatly enhanced in LAO/STO interfaces.…”

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confidence: 99%

Doping-dependent band structure of LaAlO3/SrTiO3interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission

et al. 2014

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Polarization-controlled synchrotron radiation was used to map the electronic structure of buried conducting interfaces of LaAlO 3 /SrTiO 3 in a resonant angle-resolved photoemission experiment.A strong dependence on the light polarization of the Fermi surface and band dispersions is demonstrated, highlighting the distinct Ti 3d orbitals involved in 2D conduction. Samples with different 2D doping levels were prepared and measured by photoemission, revealing different band occupancies and Fermi surface shapes. A direct comparison between the photoemission measurements and advanced first-principle calculations carried out for different 3d-band fillings is presented in conjunction with the 2D carrier concentration obtained from transport measurements.

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“…The density of states expected to show up at E F was first observed in the form of weak intensity in the band gap, reported in a resonant soft X-ray photo electron spectroscopy study [42,43]. A very recent polarization controlled, angle resolved photoelectron spectroscopy study of the STO/LAO interface [44] was successful in mapping its electronic structure and concluded that different Ti 3d orbitals are involved in the 2DEG and the mobile carriers observed in transport measurement.…”

Section: The Sto/lao Interfacementioning

confidence: 99%

Photoelectron spectroscopy of transition metal oxide interfaces

Zegenhagen

2015

Eur. Phys. J. Appl. Phys.

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Abstract. In the present paper we review applications of the photoelectron spectroscopy (PES) technique to the investigation of transition metal oxide (TMO) interfaces. We summarize very briefly some of the principle, specific characteristics of TMOs. Because of the buried nature of the interfaces, the photoelectrons must penetrate certain thicknesses of material, which is easier with higher kinetic energies in the keV range. Thus, we also briefly summarize some of the hallmarks of hard X-ray photoelectron spectroscopy (HAXPES), before presenting four explicit samples of the analysis of TMO interfaces: The LaAlO 3/SrTiO3(0 0 1) interface, which had attracted attention because of the discovery of a sheet of high mobility electrons below the thin layer of LaAlO3; superlattices of the two insulators CaCuO2 and SrTiO3, which can be prepared to become superconducting at about 40 K; epitaxial films of the 90 K superconductor GdBa2Cu3O 7−δ on NdGaO3; and finally the analysis of the nucleation of the 90 K superconductor YBa2Cu3O 7−δ on SrTiO3(0 0 1). The latter two cases of the investigation of the superconducting films are examples of photoelectron spectroscopy by X-ray standing wave (XSW) excitation. Because of this, the bare essential features of the XSW technique are also briefly reviewed.

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Spectroscopic evidence of in-gap states at the SrTiO3/LaAlO3 ultrathin interfaces

Cited by 55 publications

References 20 publications

Surface defects and conduction in polar oxide heterostructures

Surface defects and conduction in polar oxide heterostructures

Doping-dependent band structure of LaAlO3/SrTiO3interfaces by soft x-ray polarization-controlled resonant angle-resolved photoemission

Photoelectron spectroscopy of transition metal oxide interfaces

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