Conducting interfaces between amorphous oxide layers and SrTiO3(110) and SrTiO3(111)

Abstract

Interfaces between (110) and (111)SrTiO 3 (STO) single crystalline substrates and amorphous oxide layers, LaAlO 3 (a-LAO), Y:ZrO 2 (a-YSZ), and SrTiO 3 (a-STO) become conducting above a critical thickness t c . Here we show that t c for a-LAO is not depending on the substrate orientation, i.e. t c (a-LAO/(110)STO) ≈ t c (a-LAO/(111)STO) interfaces, whereas it strongly depends on the composition of the amorphous oxide: t c (a-LAO/(110)STO) < t c (a-YSZ/(110)STO) < t c (a-STO/(110)STO). It is concluded that the formation of oxygen vacancies in amorphous-type interfaces is mainly determined by the oxygen affinity of the deposited metal ions, rather than orientationaldependent enthalpy vacancy formation and diffusion. Scanning transmission microscopy characterization of amorphous and crystalline LAO/STO(110) interfaces shows much higher amount of oxygen vacancies in the former, providing experimental evidence of the distinct mechanism of conduction in these interfaces.

Tuning the Two-Dimensional Electron Gas at Oxide Interfaces with Ti–O Configurations: Evidence from X-ray Photoelectron Spectroscopy

“…So far, generating oxide 2DEGs by redox reactions has been largely limited to the STO substrate, for which various capping layers have been adopted, such as a-LAO, 22 amorphous CaHfO3, 20 yttria-stabilized zirconia (YSZ), 18 and Al2O3. 4,19 Besides (001)-oriented STO substrates, STO with orientations of (110) and (111) 27 has also been used for the deposition of a-LAO. Recently, Sarkar et al 28 replaced the STO substrate of a-LAO/STO heterostructures with anatase TiO2 [TiO2(A)] and rutile TiO2 [TiO2(R)] and obtained interfacial 2DEGs with different transport properties from a-LAO/STO.…”

Tuning the Two-Dimensional Electron Liquid at Oxide Interfaces by Buffer-Layer-Engineered Redox Reactions

“…Notably, strong redox reactions can occur when growing perovskite oxides (ABO3) capping films having B site cations of Al, Ti, Zr, and Hf or other elements with a heat of metal oxide formation lower than -350 kJ per mole of oxygen, and a work function, φ, in the range of 3.75 eV < φ < 4.4 eV 21,22 . The room temperature synthesis generally leads to disordered (d) or amorphous-like film growth, and 2DELs have been observed for heterostructures of STO capped with disordered LaAlO3 (d-LAO), disordered yttria-stabilized zirconia (d-YSZ), and disordered strontium titanate (d-STO) 16,21,[23][24][25] . This approach is applicable to not only (001)-oriented but also (110) and (111)-oriented STO crystals 25 .…”

“…The room temperature synthesis generally leads to disordered (d) or amorphous-like film growth, and 2DELs have been observed for heterostructures of STO capped with disordered LaAlO3 (d-LAO), disordered yttria-stabilized zirconia (d-YSZ), and disordered strontium titanate (d-STO) 16,21,[23][24][25] . This approach is applicable to not only (001)-oriented but also (110) and (111)-oriented STO crystals 25 .…”

“…Nevertheless, these oxygen vacancy dominated 2DELs are characterized by a pronounced carrier freeze out effect, and it remains also challenging to control their formation without a compromise in the properties 16,21,[23][24][25] .…”

X‐Ray Writing of Metallic Conductivity and Oxygen Vacancies at Silicon/SrTiO3 Interfaces

“…[12][13][14][15][16][17][18] Later on, formation of 2DEG has been realized by capping STO substrate with non-polar amorphous LAO, STO and yttria-stabilized zirconia. [12,19,20] However, this approach requires the use of techniques, such as pulsed laser deposition or molecular beam epitaxy, which are expensive to be implemented on industrial scales. Despite that, previous studies showed that the atomic layer deposition method has already been used to create all-oxide transistors with outstanding high-frequency characteristics.…”