Gallium oxide (Ga 2 O 3 ) is an ultra‐wide bandgap semiconductor with several polymorphs, among which the orthorhombic κ‐phase is particularly attractive for high‐power electronics, non‐volatile memory, and charge‐tunable devices due to its large spontaneous polarization and potential ferroelectric behavior. However, commonly grown κ‐Ga 2 O 3 thin films contain nanoscale rotational domains, hindering the characterization of intrinsic properties and complicating device integration. In this work, we present the first combined experimental and theoretical Raman spectroscopy study of single‐domain κ‐Ga 2 O 3 thin films grown on orthorhombic ε‐GaFeO 3 substrates. Using polarization‐ and angle‐resolved Raman spectroscopy, we identify over 100 phonon modes, which correlate with 117 modes calculated via density functional perturbation theory. A systematic nomenclature is introduced based on mode symmetry and frequency to aid identification and comparison across future studies. Direct comparison with rotational‐domain samples shows that single‐domain films exhibit pronounced angle‐dependent Raman intensities consistent with theoretical selection rules, features that are obscured in multi‐domain films due to domain averaging. These findings establish polarization angle‐resolved Raman spectroscopy as an effective alternative to XRD and TEM for domain structure analysis and provide a robust framework for further studies of κ‐Ga 2 O 3 in electronic applications.

Wafer-scale growth of two-dimensional semiconductors remains a key challenge for their integration into photonic technologies. While most studies of two-dimensional semiconductors have focused on transition metal dichalcogenides and their scalable fabrication, comparatively little attention has been given to III-VI monochalcogenides. Here, we report wafer-scale growth of gallium selenide (GaSe) by metal-organic chemical vapor deposition (MOCVD) and investigate its structural and optical properties for visible-range classical and quantum light emission. Two samples with thicknesses ranging from a few monolayers to several micrometers, controlled via the growth time, were investigated. The 30-minute grown sample yields intense, broad photoluminescence spanning 1.7–2.0eV, whereas the thinner 3-minute sample exhibits discrete narrow emission lines and single-photon emission with (g^(2)(0) = 0.15 ± 0.10). Remarkably, cathodoluminescence mapping reveals pronounced spatial localization of both spectrally narrow and broad emission centers. Together with temperature-dependent power-law analysis and Raman mapping, our results indicate defect-induced emission rather than intrinsic excitonic recombination. These findings establish wafer-scale MOCVD grown 2D GaSe as a platform for classical and non-classical light sources and highlight defect-engineered localization as a route toward scalable quantum photonics.

Gallium oxide (Ga2O3) is an ultra-wide bandgap semiconductor with several polymorphs, among which the orthorhombic kappa-phase is particularly attractive for high-power electronics, non-volatile memory, and charge-tunable devices due to its large spontaneous polarization and potential ferroelectric behavior. However, commonly grown kappa-Ga2O3 thin films contain nanoscale rotational domains, hindering the characterization of intrinsic properties and complicating device integration. In this work, we present the first combined experimental and theoretical Raman spectroscopy study of single-domain kappa-Ga2O3 thin films grown on orthorhombic epsilon-GaFeO3 substrates. Using polarization- and angle-resolved Raman spectroscopy, we identify over 100 phonon modes, which correlate with 117 modes calculated via density functional perturbation theory. A systematic nomenclature is introduced based on mode symmetry and frequency to aid identification and comparison across future studies. Direct comparison with rotational-domain samples shows that single-domain films exhibit pronounced angle-dependent Raman intensities consistent with theoretical selection rules, features that are obscured in multi-domain films due to domain averaging. These findings establish polarization angle-resolved Raman spectroscopy as an effective alternative to XRD and TEM for domain structure analysis and provide a robust framework for further studies of kappa-Ga2O3 in electronic applications.

The luminescence of InxGa1-xN nanowires (NWs) is frequently reported with large red-shifts as compared to the theoretical value expected from the average In content. Both compositional fluctuations and radial built-in fields were considered accountable for this effect, depending on the size, structure, composition, and surrounding medium of the NWs. In the present work, the emission properties of InGaN/GaN NWs grown by plasma-assisted molecular beam epitaxy are investigated in a comprehensive study combining ultraviolet-Raman and photoluminescence spectroscopy (PL) on vertical arrays, polarization-dependent PL on bundles of a few NWs, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and calculations of the band profiles. The roles of inhomogeneous In distribution and radial fields in the context of optical emission properties are addressed. The radial built-in fields are found to be modest, with a maximum surface band bending below 350 meV. On the other hand, variations in the local In content have been observed that give rise to potential fluctuations whose impact on the emission properties is shown to prevail over band-bending effects. Two luminescence bands with large positive and moderate negative polarization ratios of ≈+80% and ≤-60%, respectively, were observed. The red-shift in the luminescence is associated with In-rich inclusions in the NWs due to thermodynamic decomposition during growth. The negative polarization anisotropy is suggested to result from spontaneously formed superlattices in the In-rich regions of the NWs. The NWs show a preferred orthogonal absorption due to the dielectric boundary conditions and highlight the extreme sensitivity of these structures towards light polarization.

Ternary semiconductors such as InGaN thin films, quantum wells, and superlattices commonly exhibit alloy fluctuations that become increasingly pronounced with higher In-content. The thickness fluctuations of quantum wells and their thin cap-layers further introduce nanoscale inhomogeneities that alter the potential landscape. In this work, we present a combined theoretical and experimental study of InGaN single quantum wells with thin GaN cap-layers to unravel the influence of cap-layer thickness, compositional inhomogeneity, and thickness fluctuations on their electronic and optical properties. A pronounced spectral shift of quantum well emission for thin cap-layers between 1 and 10 nm is observed by micro-photoluminescence spectroscopy. The origin of this shift is explained by calculations of electronic band profiles and probability density overlap of carriers in the quantum well. The impact of alloy fluctuations and homogeneity for different cap-layer thicknesses is studied on both the microscale and nanoscale using UV micro-Raman scattering and tip-enhanced Raman spectroscopy (TERS). On the microscale, the alloy composition as determined by micro-Raman mapping appears very homogeneous except for the thinnest 1 nm cap-layer where small fluctuations are visible. On the nanoscale, TERS reveals local fluctuations on a 20–30 nm length scale. The influence of the cap-layer thickness on the TERS spectra is discussed regarding both the nanoscale homogeneity and the depth resolution of the near-field Raman scattering technique. Our results demonstrate the capabilities of TERS to resolve nanoscale thickness fluctuations and compositional inhomogeneities in ultra-thin semiconductor layers, even when they are buried by thin cap-layers with thicknesses below 10 nm.

Continuous manufacturing is becoming the new technological standard in the pharmaceutical industry. In this work, a twin-screw processor was employed for the continuous production of liquisolid tablets containing either simethicone or a combination of simethicone with loperamide hydrochloride. Both active ingredients present major technological challenges, as simethicone is a liquid, oily substance, and loperamide hydrochloride was used in a very small amount (0.27% w/w). Despite these difficulties, the use of porous tribasic calcium phosphate as a carrier and the adjustment of the settings of the twin-screw processor enabled the optimization of the characteristics of the liquid-loaded powders and made it possible to efficiently produce liquisolid tablets with advantages in physical and functional properties. The application of chemical imaging by means of Raman spectroscopy allowed for the visualization of differences in the distribution of individual components of the formulations. This proved to be a very effective tool for identifying the optimum technology to produce a drug product.

The influence of self-assembled short-period superlattices (SPSLs) on the structural and optical properties of InGaN/GaN nanowires (NWs) grown by PAMBE on Si (111) was investigated by STEM, EDXS, µ-PL analysis and k·p simulations. STEM analysis on single NWs indicates that in most of the studied nanostructures, SPSLs self-assemble during growth. The SPSLs display short-range ordering of In-rich and In-poor InxGa1-xN regions with a period of 2–3 nm that are covered by a GaN shell and that transition to a more homogenous InxGa1-xN core. Polarization- and temperature-resolved PL analysis performed on the same NWs shows that they exhibit a strong parallel polarized red-yellow emission and a predominantly perpendicular polarized blue emission, which are ascribed to different In-rich regions in the nanostructures. The correlation between STEM, µ-PL and k·p simulations provides better understanding of the rich optical emission of complex III-N nanostructures and how they are impacted by structural properties, yielding the significant impact of strain on self-assembly and spectral emission.

We investigate the compositional homogeneity of InGaN thin films with a high In content grown by migration-enhanced plasma-assisted metal-organic chemical vapor deposition. Micro-Raman spectroscopy and tip-enhanced Raman spectroscopy (TERS) are used to analyze the local InGaN composition on the micro- and nanoscale. Based on conventional micro-Raman mapping, the InGaN composition for all samples appears uniform but shows indications for intrinsic phase separations. TERS, a nanoscopic technique with a high spatial resolution far below the diffraction limit, verifies the formation of nanoscale compositional inhomogeneities. The dimensions of these compositional fluctuations observed in TERS are confirmed by scattering-type scanning near-field infrared nanoscopy (s-SNIN). In contrast to s-SNIN, we show that TERS furthermore enables the quantification of the In content in the different compositional regions and even allows the identification of InN nanoclusters near the surface of the epitaxial films.

We report a detailed study of the strong near-field Raman scattering enhancement which takes place in tip-enhanced Raman scattering (TERS) in indium nitride. In addition to the well-known first-order optical phonons of indium nitride, near-field Raman modes, not detectable in the far-field, appear when approaching the plasmonic probe. The frequencies of these modes coincide with calculated energies of second order combinational modes consisting of optical zone center phonons and acoustic phonons at the edge of the Brillouin zone. The appearance of strong combinational modes suggests that TERS in indium nitride represents a special case of Raman scattering in which a resonance condition on the nanometer scale is achieved between the localized surface plasmons (LSPs) and surface plasmon polaritons (SPPs) of the probe with the surface charge oscillation of the material. We suggest that the surface charge accumulation (SCA) in InN, which can render the surface a degenerate semiconductor, is the dominating reason for the unusually large enhancement of the TERS signal as compared to other inorganic semiconductors. Thus, the plasmon-resonant TERS (PR-TERS) process in InN makes this technique an excellent tool for defect characterization of indium-rich semiconductor heterostructures and nanostructures with high carrier concentrations.