Influence of charge compensation mechanisms on the sheet electron density at conducting LaAlO3/SrTiO3-interfaces

Gunkel, Felix; Brinks, Peter; Hoffmann‐Eifert, Susanne; Dittmann, Ralf W.; Huijben, Mark; Kleibeuker, J.E.; Koster, Gertjan; Rijnders, Guus; Waser, Rainer

doi:10.1063/1.3679139

Cited by 54 publications

(95 citation statements)

References 19 publications

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“…Gate tunable superconductivity [2,3], strong spin-orbit coupling [4,5] and magnetism [6,7] are some of the many phenomena observed. The origin of this 2DES is a long standing question in the solid state community and recent results indicate that a consistent picture should take into account both the built-in polar field and the presence of point defects [8][9][10]. Among these, oxygen vacancies and cation off-stoichiometry in STO are capable of inducing a 2DES [11,12].…”

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confidence: 99%

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Mattoni

Baek²,

Manca

et al. 2017

ACS Appl. Mater. Interfaces

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Interfaces between complex oxides constitute a unique playground for 2D electron systems (2DES), where superconductivity and magnetism can arise from combinations of bulk insulators. The 2DES at the LaAlO 3 /SrTiO 3 interface is one of the most studied in this regard, and its origin is determined by both the presence of a polar field in LaAlO 3 and the insurgence of point defects, such as oxygen vacancies and intermixed cations. These defects usually reside in the conduction channel and are responsible for a decreased electronic mobility. In this work, we use an amorphous WO 3 overlayer to control the defect formation and obtain an increased electron mobility in WO 3 /LaAlO 3 /SrTiO 3 heterostructures. The studied system shows a sharp insulator-to-metal transition as a function of both LaAlO 3 and WO 3 layer thickness. Low-temperature magnetotransport reveals a strong magnetoresistance reaching 900% at 10 T and 1.5 K, the presence of multiple conduction channels with carrier mobility up to 80 000 cm 2 V −1 s −1 and an unusually high effective mass of 5.6 me. The amorphous character of the WO 3 overlayer makes this a versatile approach for defect control at oxide interfaces, which could be applied to other heterestrostures disregarding the constraints imposed by crystal symmetry.The formation of a two-dimensional electron system (2DES) at the interface between band insulators SrTiO 3 (STO) and LaAlO 3 (LAO) is among the most intriguing effects studied in oxide electronics [1]. Gate tunable superconductivity [2,3], strong spin-orbit coupling [4,5] and magnetism [6,7] are some of the many phenomena observed. The origin of this 2DES is a long standing question in the solid state community and recent results indicate that a consistent picture should take into account both the built-in polar field and the presence of point defects [8][9][10]. Among these, oxygen vacancies and cation off-stoichiometry in STO are capable of inducing a 2DES [11,12]. However, defects residing in the conductive channel are usually responsible for a decreased electronic mobility [13]. In order to promote high electron mobility, it is crucial to confine donor sites away from the conducting plane, without preventing the 2DES formation in the STO top layers. Previous attempts to control the defect concentration profile and thus enhance the mobility involved the use of crystalline insulating overlayers [14,15] [18,19]. A promising material to control defect formation is tungsten oxide WO 3 . The several possible oxidations states of tungsten make WO 3 particularly active in undergoing redox reactions. For this reason this material is often utilized in electrochemical applications and electrochromic devices [20][21][22]. Also, both crystalline and amorphous WO 3 can host vacancies and interstitial atoms, thus allowing cation accommodation and diffusion, with a tendency to form compounds such as tungsten bronzes [23,24]. Recent progress demonstrated the high-quality growth of WO 3 thin films on perovskite materials [25][26][27].In this work we co...

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Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Mattoni

Baek²,

Manca

et al. 2017

ACS Appl. Mater. Interfaces

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“…Such phenomenon is frequently found in perovskites such as La 23,24 Also the role of Sr-vacancies at the LaAlO 3 /SrTiO 3 interface is under discussion. 25 The Sr segregation effect occurs for all heterostructures and film thicknesses addressed in our investigation.…”

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Observation of strontium segregation in LaAlO3/SrTiO3 and NdGaO3/SrTiO3 oxide heterostructures by X-ray photoemission spectroscopy

et al. 2014

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LaAlO3 and NdGaO3 thin films of different thicknesses have been grown by pulsed laser deposition on TiO2-terminated SrTiO3 single crystals and investigated by soft X-ray photoemission spectroscopy. The surface sensitivity of the measurements has been tuned by varying photon energy hν and emission angle Θ. In contrast to the core levels of the other elements, the Sr 3d line shows an unexpected splitting for higher surface sensitivity, signaling the presence of a second strontium component. From our quantitative analysis we conclude that during the growth process Sr atoms diffuse away from the substrate and segregate at the surface of the heterostructure, possibly forming strontium oxide.

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“…1) 3,4 . The other three mechanisms involve various defects, including the oxygen vacancies at the interface (denoted as V O (I), where 'I' means 'Interface') [14][15][16] , oxygen vacancies at LaAlO 3 overlayer surface (denoted as V O (S), where S means 'Surface') [17][18][19][20][21][22] , and the La-onSr (La Sr ) antisite donor defects induced by interfacial cation intermixing [23][24][25][26][27][28][29] . As Table 1 shows, each of these proposed mechanisms represents one aspect of the interface physics, explains some experimental findings, but conflicts with a few others 2 .…”

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A polarity-induced defect mechanism for conductivity and magnetism at polar–nonpolar oxide interfaces

2014

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The discovery of conductivity and magnetism at the polar-nonpolar interfaces of insulating nonmagnetic oxides such as LaAlO 3 and SrTiO 3 has raised prospects for attaining interfacial functionalities absent in the component materials. Yet, the microscopic origin of such emergent phenomena remains unclear, posing obstacles to design of improved functionalities. Here we present first principles calculations of electronic and defect properties of LaAlO 3 / SrTiO 3 interfaces and reveal a unifying mechanism for the origins of both conductivity and magnetism. We demonstrate that the polar discontinuity across the interface triggers thermodynamically the spontaneous formation of certain defects that in turn cancel the polar field induced by the polar discontinuity. The ionization of the spontaneously formed surface oxygen vacancy defects leads to interface conductivity, whereas the unionized Ti-on-Al antisite defects lead to interface magnetism. The proposed mechanism suggests practical design principles for inducing and controlling both conductivity and magnetism at general polar-nonpolar interfaces.

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Influence of charge compensation mechanisms on the sheet electron density at conducting LaAlO3/SrTiO3-interfaces

Cited by 54 publications

References 19 publications

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Observation of strontium segregation in LaAlO3/SrTiO3 and NdGaO3/SrTiO3 oxide heterostructures by X-ray photoemission spectroscopy

A polarity-induced defect mechanism for conductivity and magnetism at polar–nonpolar oxide interfaces

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Influence of charge compensation mechanisms on the sheet electron density at conducting LaAlO3/SrTiO3-interfaces

Cited by 54 publications

References 19 publications

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

Observation of strontium segregation in LaAlO3/SrTiO3 and NdGaO3/SrTiO3 oxide heterostructures by X-ray photoemission spectroscopy

A polarity-induced defect mechanism for conductivity and magnetism at polar–nonpolar oxide interfaces

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Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO₃ Overlayers