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

Abstract

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.

Evaluation of Optical and Acoustical Properties of Ba1−xSrxTiO3 Thin Film Material Library via Conjugation of Picosecond Laser Ultrasonics with X-ray Diffraction, Energy Dispersive Spectroscopy, Electron Probe Micro Analysis, Scanning Electron and Atomic Force Microscopies

“…We can estimate from the 128 GHz BF (Figure 4b) that the refractive index n STO (356 nm) ≈ 2.91. This value is consistent with the one quite recently measured by spectroscopic ellipsometry [54,55]. These preliminary experiments are important for the future comparison of the acoustic and optical properties of bulk STO with those from the STO in the laterally graded Ba 1−x Sr x TiO 3 (BSTx) library, i.e., at x = 0 composition point.…”

“…Therefore, the difference between the Brillouin frequencies at the STO edge of the library and the Brillouin frequencies in bulk STO is predominantly due to the difference in their refractive indices. When approaching the STO edge of the BSTx library, the measured refractive index (Figure 6f) at the UV probe wavelength (n UV,STO BSTx ≈ 2.5) is lower than in bulk STO, measured by us in the STO substrate in Section 2.2.2. and reported in the literature [51][52][53][54][55] (n UV STO ≈ 2.9). A commonly accepted explanation for the difference in the optical refractive indices of the films prepared by PLD from those in bulk materials is the deviation from the ideal stoichiometry, which results in the increase of lattice parameters accompanied by the modification of the free charge carrier density, the variation in the impurity bands and shift of the charge transfer optical energies.…”

Ultrafast strain engineering and coherent structural dynamics from resonantly driven optical phonons in LaAlO3

“…A high efficiency of ionic Raman scattering is anticipated in LaAlO 3 as mutual coupling between optical phonon modes exists and even results in a small negative Lyddane-Sachs-Teller splitting between longitudinal and transverse optical modes 25 . The wide bandgap of LaAlO 3 (5.6 eV 26 ) as well as the absence of electronic in-gap states 27 ensures the purely structural nature of the photo-induced response.…”

“…2c). In transparent materials, the frequency of the oscillations f is related to the refractive index n of the material at the probe wavelength 27 , the speed of sound v s , the angle θ w.r.t. the sample normal and the wavelength λ of the probe by the relation 29 f ¼ 2nv s cosðθÞ=λ.…”

Tunable shear strain from resonantly driven optical phonons

“…The tuning of the pump photon energy was done in the range 70-180 meV and allowed us to compare dynamics excited in the optical transparency window, with structural transient dynamics induced by pulses tuned in resonance with the lattice vibrational mode. The wide bandgap of LaAlO 3 (5.6 eV 15 ), as well as the absence of electronic in-gap states 16 , ensures the purely structural nature of the photoinduced response. Time-resolved optical reflectivity and birefringence measurements are performed using near infrared probe pulses (100 fs, 1.5 eV, 1 kHz), in two complementary experimental geometries, schematically illustrated in Fig.…”