Surface defects and conduction in polar oxide heterostructures

Bristowe, Nicholas C.; Littlewood, P. B.; Artacho, Emilio

doi:10.1103/physrevb.83.205405

Cited by 164 publications

(223 citation statements)

References 38 publications

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“…As far as surface adsorbates are concerned, they may interact with surface atoms or oxygen defects, and cause complex surface states. Two recent theoretical papers have suggested that the dissociation of hydrogen 21 and redox reactions 22 on the LaAlO 3 sur- (1) (1) face as possible electron sources. In both cases, V Uncom is reduced compared with that of the idealized surface.…”

Section: Comparison Between Sap and Adsorption Of Solvent Vapourmentioning

confidence: 99%

“…The intense interest in the LaAlO 3 /SrTiO 3 interface [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] has led to several recent experimental observations that suggest a close relationship between the interface and the LaAlO 3 surface. These include the use of conducting atomic force microscopy probes to toggle a metal insulator transition [10][11][12] through the writing of surface charge 12,13 , and the use of capping layers of SrTiO 3 (ref.…”

mentioning

confidence: 99%

“…15) to alter the interface conductivity. The origin of these effects, and indeed the interface conductivity itself, remains in debate 4,[16][17][18][19][20][21][22] . The transfer of electrons from the surface to the interface, to reconcile the polar discontinuity between the neutral {100} layers in SrTiO 3 and the charged layers in {100} LaAlO 3 , is one model that naturally connects the electronic states of the interface and LaAlO 3 surface 4,18-22 .…”

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Control of electronic conduction at an oxide heterointerface using surface polar adsorbates

et al. 2011

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The interface between LaAlo 3 and srTio 3 possesses a range of intriguing properties, notably a proposed connection between the surface state of the LaAlo 3 and the conductivity buried in the srTio 3 . Here we study the effect of the surface adsorption of a variety of common laboratory solvents on the conductivity at the interface between LaAlo 3 and srTio 3 . We show that the application of chemicals such as acetone, ethanol, and water can induce a large change in the conductivity, and, in particular, an insulator to metal transition around the critical LaAlo 3 thickness. This phenomenon is observed only for polar solvents. These data provide experimental evidence for a general polarization-facilitated electronic transfer mechanism.

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Section: Comparison Between Sap and Adsorption Of Solvent Vapourmentioning

confidence: 99%

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Control of electronic conduction at an oxide heterointerface using surface polar adsorbates

et al. 2011

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“…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.…”

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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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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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“…[1] Several unexpected physical properties have been experimentally observed, [2,3] which stimulated numerous theoretical investigations. [4][5][6] However, despite intense research, the exact origin of such remarkable behavior remains to be understood. While the polar catastrophe model at the interface between a polar (LAO) and a non-polar (STO) oxide provides an appealing explanation for the characteristics of this system, [7] the role of extrinsic factors such as oxygen vacancies and/or cation intermixing in producing similar behavior cannot be ruled out.…”

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Atomic Layer Engineering of Perovskite Oxides for Chemically Sharp Heterointerfaces

et al. 2012

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Keywords: perovskite oxide interface, pulsed laser deposition, LaAlO 3 /SrTiO 3 , atomic layer engineering, epitaxial strain 2 The two-dimensional (2D) conducting interface between LaAlO 3 (LAO) and SrTiO 3 (STO) -both perovskite oxide band insulators -has attracted immense attention since its discovery by Ohtomo and Hwang. [1] Several unexpected physical properties have been experimentally observed, [2,3] which stimulated numerous theoretical investigations. [4][5][6] However, despite intense research, the exact origin of such remarkable behavior remains to be understood. While the polar catastrophe model at the interface between a polar (LAO) and a non-polar (STO) oxide provides an appealing explanation for the characteristics of this system, [7] the role of extrinsic factors such as oxygen vacancies and/or cation intermixing in producing similar behavior cannot be ruled out. [8][9][10][11][12][13][14][15] Pulsed laser deposition (PLD) is the most frequently used method for fabricating LAO/STO heterostructures. It is generally understood that, among the various growth parameters, the background gas pressure and the substrate temperature have the greatest influence on the film quality. Under optimal conditions -i.e., when the oxygen partial pressure P(O 2 ) is used to tune the kinetic energy of growth species in the laser-induced plume -single crystal thin films with atomically smooth surfaces can be grown. [16] However, at less than optimal growth conditions, the highly energetic plume-substrate interactions can produce undesirable departures from stoichiometry. [17,18] As summarized in Table 1 of Supporting Information, the PLD growth conditions used in published reports on the LAO/STO interface formation were not uniform, suggesting that the differences in the growth parameters might contribute to inconsistent observations and/or interpretations of interface conductivity. Most importantly, compared to conventional PLD growth conditions for typical perovskite oxides, [19,20] many LAO/STO heterostructures were grown at unusually low P(O 2 ) and rather high temperatures. 3The selective use of low P(O 2 ) in the early stage of LAO/STO growth raises an intriguing question: what if instead very high P(O 2 ) was used to grow the LAO film? It was shown that LAO/STO growth at low P(O 2 ) easily generates a high concentration of oxygen vacancies, [8][9][10][11] and post-annealing in a high-pressure oxygen ambient was found to reduce their number. [3,8,9] Interestingly, some previous work reported good metallic conduction even after post-annealing, suggesting that the contribution of oxygen vacancies to the electronic conduction is negligible. [1,7,21] It should be further noted that the energetic process of PLD -i.e., species are transported from the target to the substrate with a high kinetic energy -may substantially influence the formation of cation off-stoichiomety, resulting in a chemically broadened interface. [12][13][14][15] Here again, the P(O 2 ) should have a strong influence on interface formation, but onl...

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Surface defects and conduction in polar oxide heterostructures

Cited by 164 publications

References 38 publications

Control of electronic conduction at an oxide heterointerface using surface polar adsorbates

Control of electronic conduction at an oxide heterointerface using surface polar adsorbates

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

Atomic Layer Engineering of Perovskite Oxides for Chemically Sharp Heterointerfaces

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Surface defects and conduction in polar oxide heterostructures

Cited by 164 publications

References 38 publications

Control of electronic conduction at an oxide heterointerface using surface polar adsorbates

Control of electronic conduction at an oxide heterointerface using surface polar adsorbates

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

Atomic Layer Engineering of Perovskite Oxides for Chemically Sharp Heterointerfaces

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