Lattice parameters and Raman-active phonon modes of β-(AlxGa1−x)2O3

Abstract

We present X-ray diffraction and Raman spectroscopy investigations of a (100)-oriented (AlxGa1–x)2O3 thin film on MgO (100) and bulk-like ceramics in dependence on their composition. The thin film grown by pulsed laser deposition has a continuous lateral composition spread allowing to determine precisely the dependence of the phonon mode properties and lattice parameters on the chemical composition. For x < 0.4, we observe the single-phase β-modification. Its lattice parameters and phonon energies depend linearly on the composition. We determined the slopes of these dependencies for the individual lattice parameters and for nine Raman lines, respectively. While the lattice parameters of the ceramics follow Vegard's rule, deviations are observed for the thin film. This deviation has only a small effect on the phonon energies, which show a reasonably good agreement between thin film and ceramics.

Dielectric function in the spectral range (0.5–8.5)eV of an (Alx Ga1−x)2O3 thin film with continuous composition spread

“…Some exception can be observed for x > 0.4, which we can relate to the occurrence of c-phase material. 32 The general lineshape resembles that of pure b-Ga 2 O 3 ; 12,14,15 thus, we conclude that the materials' electronic structure is dominantly b-Ga 2 O 3 -like for all Al concentrations investigated. A clear blue-shift of all absorption features can be observed as expected due to the much larger band gap of a-and c-Al 2 O 3 of %9 eV.…”

“…The increase of the transition energies, besides the effect of Al incorporation on the electronic structure, also resembles the behaviour of the lattice constants and the phonon modes. 32 Especially, the bowing observed for the thin film in the a-lattice constant, which we relate to internal strain, can be considered to be partially responsible for the bowing observed in the x-dependence of the transition energies. As a general trend, the broadening parameter of the TcLo function increases with the increase in transition energy from %0:2 eV to %1:5 eV, but does almost not depend on x.…”

“…More details on the growth conditions can be found in Ref. 32. As also detailed there, the composition as a function of the position on the wafer and the structural properties of the thin films have been investigated by means of energy dispersive X-Ray spectroscopy (EDX), X-Ray diffraction (XRD), and Raman spectroscopy.…”

“…Spectra of the absorption coefficient a in the UV spectral range calculated from the B-spline MDF in a (a) linear and (b) logarithmic scale.Dashed lines indicate composition for which the c-phase has been observed 32. Dashed black lines indicate the linear approximation and extrapolation of log a towards zero.…”

Temperature dependence of Raman scattering in β-(AlGa)2O3 thin films

“…[9][10][11][12] Therefore, it has been widely employed in semiconductors. Kranert et al 13 have reported Raman spectra of (AlGa) 2 O 3 films with different Al content (0-0.55) at room temperature. However, in contrast to the comprehensive investigation of temperature effect of Raman scattering for other semiconductors, 14,15 temperature dependence of phonon behavior in β-(AlGa) 2 O 3 thin films has not been reported up to now.…”