The Raman spectrum and particularly the Raman scattering intensities of monoclinic β-Ga2O3 are investigated by experiment and theory. The low symmetry of β-Ga2O3 results in a complex dependence of the Raman intensity for the individual phonon modes on the scattering geometry which is additionally affected by birefringence. We measured the Raman spectra in dependence on the polarization direction for backscattering on three crystallographic planes of β-Ga2O3 and modelled these dependencies using a modified Raman tensor formalism which takes birefringence into account. The spectral position of all 15 Raman active phonon modes and the Raman tensor elements of 13 modes were determined and are compared to results from ab-initio calculations.

We present a formalism for calculating the Raman scattering intensity dependent on the polarization configuration for optically anisotropic crystals. It can be applied to crystals of arbitrary orientation and crystal symmetry measured in normal incidence backscattering geometry. The classical Raman tensor formalism cannot be used for optically anisotropic materials due to birefringence causing the polarization within the crystal to be depth dependent. We show that in the limit of averaging over a sufficiently large scattering depth, the observed Raman intensities converge and can be described by an effective Raman tensor given here. Full agreement with experimental results for uniaxial and biaxial crystals is demonstrated.

We present X-ray diffraction and Raman spectroscopy investigations of (InxGa1–x)2O3 thin films and bulk-like ceramics in dependence of their composition. The thin films grown by pulsed laser deposition have a continuous lateral composition spread allowing the determination of phonon mode properties and lattice parameters with high sensitivity to the composition from a single 2-in. wafer. In the regime of low indium concentration, the phonon energies depend linearly on the composition and show a good agreement between both sample types. We determined the slopes of these dependencies for eight different Raman modes. While the lattice parameters of the ceramics follow Vegard's rule, deviations are observed for the thin films. Further, we found indications of the high-pressure phase InGaO3 II in the thin films above a critical indium concentration, its value depending on the type of substrate.

We report on structural and optical properties of a (In x Ga −x 1 ) 2 O 3 thin film having a monotonic lateral variation of the indium content x ( ⩽ ⩽ x 0 0.9). The growth condition for each In content is similar allowing precise determination of the dependence of material properties on x. For low In content ( < x 0.15) the thin film has monoclinic crystal structure; for highest In contents ( > x 0.8) the cubic bixbyite phase is predominant. For intermediate alloying we observe additionally the rhombohedral InGaO 3 (II) crystallographic phase. The optical band-gap decreases systematically with increasing indium content and has a linear dependency on x for parts of the sample having the monoclinic phase, only. Further, properties of Pt Schottky diodes are reported for monoclinic (In x Ga −x 1 ) 2 O 3 and photo response measurements for < x 0.1

We introduce a symmetry assignment for the Raman active phonon modes for the cubic modification of indium sesqui‐oxide In2O3. Using a resonant excitation at $\lambda _{\rm exc} = 325\;{\rm nm},$ we observed 19 out of 22 expected first‐order Raman modes, of which many have not been reported before. This knowledge on the Raman spectrum is crucial for the interpretation of obtained Raman spectra, both resonantly and non‐resonantly ex‐ cited, and for the material characterization based on it. The phonon mode symmetry was determined based on polarized measurements on two In2O3 thin films with (001) and (111) orientation. The measurements were carried out at T = 10 K to minimize the linewidth for the separation of spectrally close lines. Besides the energy of the different phonon modes, we give their linewidths and relative intensities. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)