Optical constants, band gap, and infrared-active phonons of (LaAlO3)0.3(Sr2AlTaO6)0.35 (LSAT) from spectroscopic ellipsometry

Nunley, T. Nathan; Willett-Gies, Travis I.; Cooke, Jacqueline; Manciu, Felicia; Maršík, Přemysl; Bernhard, C.; Zollner, Stefan

doi:10.1116/1.4960356

Cited by 19 publications

(13 citation statements)

References 31 publications

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“…coefficient as a function of photon energy obtained with the multi-oscillator model developed for the LSAT substrate. Our results are in good agreement with previous results [30]; however, by characterizing the substrate further in the VUV range, we have more complete picture of the optical properties of this material. Upon closer examination of the absorption coefficient in the range α from 2×10 3 cm −1 to 45×10 3 cm −1 , we find that plotting the square root of absorption versus photon energy results again in stepwise linear behavior, which as stated above for STO is indicative of an indirect bandgap for LSAT.…”

Section: Lanthanum Strontium Aluminum Tantalatesupporting

confidence: 92%

“…al. [29] (5.6 eV), but deviates a bit more from other work [30] (5.8 eV). The development of thermally-stable single-crystal rare-earth scandates such as dysprosium scandate, DyScO 3 (DSO), was initially motivated by studies focused on the strain-induced enhancements of superconducting thin films which required an array of substrate materials with a range of available lattice parameters that fit neatly within the window set by STO and barium titanate (3.905 -4.036 Å) [22,23,53].…”

Section: Lanthanum Strontium Aluminum Tantalatecontrasting

confidence: 72%

“…Additionally, STO substrate is well-analyzed by Zollner et al [26]; nevertheless, it is necessary to present our spectra here in order to observe the variation of optical parameters between undoped and Nb-doped STO substrates. Optical properties of LSAT [29,30] and LAO [31][32][33] are well-defined in the IR and VIS-NUV spectral range up to 6 eV, but this spectral range is not sufficient for complete characterization as these substrates are optically transparent through the visible range and the onset of absorption occurs at photon energies up around 5 eV. In general, optical studies of epitaxial thin films in the vacuum ultra-violet range are becoming increasingly more accessible [34,35], and therefore accurate studies of these substrates are required up through the VUV range to photon energies of at least 8.8 eV.…”

Section: Introductionmentioning

confidence: 99%

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Optical NIR-VIS-VUV constants of advanced substrates for thin-film devices

Chernova

Brooks

Chvostová

et al. 2017

Opt. Mater. Express

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The optical properties of several commonly used single-crystal oxide substrates were explored by spectroscopic ellipsometry over a wide spectral range from 0.74 eV to 8.8 eV. The crystals examined are (100) SrTiO 3 , 0.7 % wt Nb-doped (100) SrTiO 3 ,(100) (LaAlO 3) 0.29 (SrAl 0.5 Ta 0.5 O 3) 0.7 , (011) DyScO 3 , (100) MgAl 2 O 4 , (100) MgO, and (100) LaAlO 3 , all of which enable epitaxial growth of numerous perovskite-type and other optical thin films. An analytic form for the complex dielectric function was derived from ellipsometric data through a physically consistent modeling process. The obtained dielectric spectra were further utilized to calculate the complex index of refraction and absorption coefficient for each substrate material. The absorption spectra and optical band gap were analyzed using Tauc plots. The parameters for reconstructing the dielectric functions are given in detail, allowing for extensive applications of the results of this work.

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Section: Lanthanum Strontium Aluminum Tantalatesupporting

confidence: 92%

Section: Lanthanum Strontium Aluminum Tantalatecontrasting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Optical NIR-VIS-VUV constants of advanced substrates for thin-film devices

Chernova

Brooks

Chvostová

et al. 2017

Opt. Mater. Express

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“…All measurements in this manuscript were performed at room temperature. [40] We point out, however, that Nunley et al [40] observed that LSAT is usually opaque for energies above 4.8 eV, which could account for the extracted gap value here. The absorption edges for the three substrates differ strongly, and the transmittance of the LSAT substrate is markedly different from that of the other two, likely due to defect states in the crystal.…”

Section: Film Growth and Structural Parametersmentioning

confidence: 53%

Revisiting the Optical Band Gap in Epitaxial BiFeO₃ Thin Films

Sando

Carrétéro

Grisolia

et al. 2017

Advanced Optical Materials

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the pursuit of electric-field-controlled magnetism. [2] BFO is part of a larger family of ferroelectric oxides, important compounds that are relevant in the fields of optical modulation, [3] data storage, [4,5] actuation, [6] and sensing. [7] While many of these established applications are based on bulk samples (either single crystals or ceramics), there has recently been a substantial drive to exploit and enhance the desirable functional properties of ferroelectric oxides in thin film form. [8][9][10] Epitaxial strain [11] is a powerful tool in this context: tuning the structure of thin films by strain can bring about, for example, strong modification of ferroelectric polarization and transition temperatures, [12] spin configurations, [13] and magnetic and magneto-transport properties. [14] A wide range of remarkable functionalities has been shown in BFO thin films, [15] such as a tuneable ferroelectric domain structure, [16] strongly strain-dependent magnetic structure, [17] and electric-field sensitive magnetic functionalities. [18,19] While the bulk parent compound of BFO is rhombohedral (R'), a peculiar aspect of thin film BFO is the formation, under strong (≈4%) compressive strain, of a giant axial ratio tetragonal-like (T') polymorph. [20,21] This change in structure is concomitant with a modification of the oxygen coordination (from octahedral to square pyramidal) and drastic changes in optical [22] and piezoelectric responses, [23] and magnetic properties. [24] From an optical point of view, BFO has a band gap that is rather low for ferroelectric oxides, [25] and it exhibits a significant bulk photovoltaic effect, [26] pushing it into the realm of optical research in the hope of using it in energy harvesting, photocatalysis or optical devices. [22] Given the significant general interest of ferroelectrics for photovoltaic applications, [27] it is important to obtain a stronger understanding of the influence of growth parameters and other factors on the optical properties of BFO thin films. In addition, significant size effects, related to microstrain and oxygen content, have been shown to influence the optical response of BFO nanoparticles. [28] Although a large body of literature regarding optical properties (particularly the band gap) for BFO in the form of thin films exists, there is a large dispersion in the data, with reported values for R' BFO ranging from 2.65 to 2.82 eV. For A detailed structural and optical band gap characterization study for more than 40 epitaxial bismuth ferrite (BiFeO 3 -BFO) thin films, measured by X-ray diffraction, atomic force microscopy, and optical transmission spectroscopy, is reported. The films are grown in different deposition systems to varying thicknesses (10-140 nm), on several substrates, and under different growth and cooling conditions. Using the results and literature data, first it is shown that the band gap measured by transmission is systematically lower than the gap found by ellipsometry, suggesting that sufficient caution must be exercised when comparing...

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“…When LSAT is grown on STO, a two-dimensional carrier gas forms at the LSAT/STO interface. 24 LSAT has a band gap of 4.9 eV, 25 smaller than the LAO band gap of 5.6 eV, 26 which can affect the relative importance of the different mechanisms contributing to the formation of the conducting gas. LSAT has a 1 % lattice mismatch with STO, as opposed to a 3 % mismatch in the case of LAO, which means the interfacial STO layers experience a smaller strain in the case of LSAT/STO.…”

mentioning

confidence: 99%

Electrostatic tuning of magnetism at the conducting (111) (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3 interface

Bal

Huang

Han

et al. 2017

Applied Physics Letters

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We present measurements of the low temperature electrical transport properties of the two dimensional carrier gas that forms at the interface of (111) (La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 )/SrTiO 3 (LSAT/STO) as a function of applied back gate voltage, V g . As is found in (111) LaAlO 3 /SrTiO 3 interfaces, the low-field Hall coefficient is electron-like, but shows a sharp reduction in magnitude below V g ∼ 20 V, indicating the presence of holelike carriers in the system. This same value of V g correlates approximately with the gate voltage below which the magnetoresistance evolves from nonhysteretic to hysteretic behavior at millikelvin temperatures, signaling the onset of magnetic order in the system. We believe our results can provide insight into the mechanism of magnetism in SrTiO 3 based systems.For more than ten years, the two dimensional carrier gas in SrTiO 3 (STO) based heterostructures has provided us with a model system to study a wide variety of physical phenomena, such as magnetism, superconductivity, spinorbit interaction, and localization effects. [1][2][3][4][5][6][7] Adding to the interest is the fact that these interfacial phenomena can be tuned by a range of experimental handles, including applied electric fields, 3 oxygen partial pressure during growth, 5,8,9 capping layers, 10 post growth annealing treatment, 11,12 crystal orientation, 14 and strain. 15 So far, most studies on these heterostructures have focused on LaAlO 3 (LAO) deposited on a (001) oriented STO substrate. However, it was recently discovered that changing the surface crystal orientation can vastly change the properties of the carrier gas.14 In particular, a tunable anisotropy in transport parameters was observed in (110) and (111) oriented LAO/STO. 12,13,[16][17][18] The (111) oriented interface has also been predicted to show novel topological phases, given that the surface Ti atoms in STO form a honeycomb lattice that hosts orbitals with hexagonal symmetry. 19-23(La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 ) (LSAT) is a commonly used substrate for the growth of other perovskite films. When LSAT is grown on STO, a two-dimensional carrier gas forms at the LSAT/STO interface.24 LSAT has a band gap of 4.9 eV, 25 smaller than the LAO band gap of 5.6 eV, 26 which can affect the relative importance of the different mechanisms contributing to the formation of the conducting gas. LSAT has a 1 % lattice mismatch with STO, as opposed to a 3 % mismatch in the case of LAO, which means the interfacial STO layers experience a smaller strain in the case of LSAT/STO. Also, unlike LAO, but similar to STO, LSAT undergoes a cubic to tetragonal transition at about 100 K, 27,28 which is also expected to reduce strain effects. Earlier work on (001) LAO/STO interfaces 15 demonstrated that strain at the interface can drastically change conduction, whereas recent studies of LSAT grown on (001) STO suggested that the lower strain compared to LAO significantly increased the carrier mobility.24,29 However, there have been only a few transport experiments performed ...

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Optical constants, band gap, and infrared-active phonons of (LaAlO3)0.3(Sr2AlTaO6)0.35 (LSAT) from spectroscopic ellipsometry

Cited by 19 publications

References 31 publications

Optical NIR-VIS-VUV constants of advanced substrates for thin-film devices

Optical NIR-VIS-VUV constants of advanced substrates for thin-film devices

Revisiting the Optical Band Gap in Epitaxial BiFeO₃ Thin Films

Electrostatic tuning of magnetism at the conducting (111) (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3 interface

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Optical constants, band gap, and infrared-active phonons of (LaAlO3)0.3(Sr2AlTaO6)0.35 (LSAT) from spectroscopic ellipsometry

Cited by 19 publications

References 31 publications

Optical NIR-VIS-VUV constants of advanced substrates for thin-film devices

Optical NIR-VIS-VUV constants of advanced substrates for thin-film devices

Revisiting the Optical Band Gap in Epitaxial BiFeO3 Thin Films

Electrostatic tuning of magnetism at the conducting (111) (La0.3Sr0.7)(Al0.65Ta0.35)/SrTiO3 interface

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Revisiting the Optical Band Gap in Epitaxial BiFeO₃ Thin Films