Herein, wafer‐scale Ga2O3 films are shown, which are synthesized by oxide printing of liquid metal Ga on SiO2/Si and sapphire substrates. This process enables highly uniform ≈2 nm‐thick films over ≫1 mm2 areas. The physical properties of these films (as‐deposited and after annealing in ambient conditions) are investigated. X‐ray photoelectron spectroscopy indicates that the as‐prepared films contain significant fractions (up to 8% wt) of Ga metal residue, which completely converts to Ga2O3 after annealing. Results from Raman spectroscopy confirm the presence of β‐phase in annealed samples. Transmission electron microscopy images indicate that the films are composed of polycrystalline domains. Photoluminescence is observed in all samples, depicting the typical spectrum of Ga2O3 with four emission bands. After annealing, the luminescence intensity increases across all samples, which is attributed to an enhancement in crystallinity. Also, the relative intensity of the blue emission decreases after annealing, which is consistent with a transition from bluish to greenish color in the films. This observation is associated with a change in defect population upon annealing. Overall, these results demonstrate that oxide printing of liquid metal gallium is a simple process that, upon annealing of the resulting films, leads to nanometer‐thin β‐Ga2O3 films over wafer‐scale areas.

Using spectroscopic ellipsometry, the authors determined the optical constants (complex dielectric function) for (LaAlO3)0.3(Sr2AlTaO6)0.35 (LSAT) from 0.01 to 6.5 eV. Above 0.5 eV, the data were described with a sum of two Tauc-Lorentz oscillators and two poles. A direct gap of 5.8 ± 0.1 eV was found. An Urbach tail extends to even lower photon energies and makes the crystal opaque above 4.8 eV. Using Fourier-transform infrared ellipsometry, the lattice dynamics was studied. Nine pairs of transverse/longitudinal phonons were found and attributed to disorder in the La/Sr sublattice, ordering in the Al/Ta sublattice, and two-phonon absorption.

We report a new type of structural defect in β-Ga2O3 homoepitaxial thin films grown by metalorganic vapor phase epitaxy, which we have dubbed as “sympetalous defects.” These consist of a line defect (for example, a nanotube defect) in the underlying substrate combined with a multi-faceted inverted polycrystalline pyramid in the epitaxial film, which may also be decorated with twinned polycrystalline grains. In plan-view atomic force, scanning electron, or optical microscopies, the sympetalous defects appear similar in shape to polygonal etch pits observed for single crystals. Photoluminescence microscopy exposed spots of polarization-dependent luminescence at these defects, different from the single crystal films' luminescence. Furthermore, some of the defects exhibited circular dichroism in their luminescence that we correlated with partial helices formed within the pits by the arrangement of linearly dichroic polycrystalline grains. Finally, the density of sympetalous defects agrees with the etch pit densities of the substrates. Understanding and controlling these defects will be of importance as they modify the local properties of films, affect fabricated device yields, and influence characterization experiments.

A c c e p t e d M a n u s c r i p tWe performed high-precision measurements of the dielectric function of strained and bulk (unstrained) Ge to determine the interband critical-point parameters. The E1 and E1+D1 critical points in a Ge layer on Si are redshifted compared to bulk Ge, due to the mismatch of the thermal expansion coefficients of Ge and Si. AbstractEpitaxial Ge layers on a Si substrate experience a tensile biaxial stress due to the difference between the thermal expansion coefficients of the Ge epilayer and the Si substrate, which can be measured using asymmetric x-ray diffraction reciprocal space maps. This stress depends on temperature and affects the band structure, interband critical points, and optical spectra. This manuscripts reports careful measurements of the temperature dependence of the dielectric function and the interband critical point parameters of bulk Ge and Ge epilayers on Si using spectroscopic ellipsometry from 80 to 780 K and from 0.8 to 6.5 eV. The authors find a temperature-dependent redshift of the E 1 and E 1 + ∆ 1 critical points in Ge on Si (relative to bulk Ge). This redshift can be described well with a model based on thermal expansion coefficients, continuum elasticity theory, and the deformation potential theory for interband transitions. The interband transitions leading to E 0 and E 2 critical points have lower symmetry and therefore are not affected by the stress.

In this work, a systematic photoluminescence (PL) study on three series of gallium oxide/aluminum gallium oxide films and bulk single crystals is performed including comparing doping, epitaxial substrates, and aluminum concentration. It is observed that blue/green emission intensity strongly correlates with extended structural defects rather than the point defects frequently assumed. Bulk crystals or Si-doped films homoepitaxially grown on (010) β-Ga2O3 yield an intense dominant UV emission, while samples with extended structural defects, such as gallium oxide films grown on either (-201) β-Ga2O3 or sapphire, as well as thick aluminum gallium oxide films grown on either (010) β-Ga2O3 or sapphire, all show a very broad PL spectrum with intense dominant blue/green emission. PL differences between samples and the possible causes of these differences are analyzed. This work expands previous reports that have so far attributed blue and green emissions to point defects and shows that in the case of thin films, extended defects might have a prominent role in emission properties.