Ordinary dielectric function of corundumlike α−Ga2O3 from 40 meV to 20 eV

Abstract

The linear optical response of metastable α-Ga 2 O 3 is investigated by spectroscopic ellipsometry. We determine the ordinary dielectric function from lattice vibrations up to the vacuum ultraviolet spectral range at room temperature for a sample with a (0001) surface. Three out of four E u infrared-active phonon modes are unambiguously determined, and their frequencies are in good agreement with density functional theory calculations. The dispersion of the refractive index in the visible and ultraviolet part of the spectrum is determined. High-energy interband transitions are characterized up to 20 eV. By comparison with the optical response of α-Al 2 O 3 and with theoretical results, a tentative assignment of interband transitions is proposed.

Ellipsometry Study of Hexagonal Boron Nitride Using Synchrotron Radiation: Transparency Window in the Far‐UVC

“…A higher bandgap of %5.6 eV has been reported for the metastable α À Ga 2 O 3 phase. [24,25] After the seminal paper by Watanabe et al, [26] which demonstrated UV lasing at 215 nm in h-BN single crystal grown under high-pressure and high-temperature conditions, a new competitor to AlN has emerged in the area of semiconductor materials for UVC applications. The first h-BN-based electroluminescent device in the deep-UV range was soon later realized.…”

Infrared dielectric functions and Brillouin zone center phonons of $α$-Ga$_2$O$_3$ compared to $α$-Al$_2$O$_3$

“…A small binding energy of 7 meV was found for the lowest ordinary transition and a hyperbolic (quasi 2-dimensional) exciton with large binding energy of 178 meV was observed for the M 1 -type (extraordinary) critical point transition. 22 In earlier work, Segura et al, 39 Kracht et al, 40 and Feneberg et al 36 reported on more limited spectroscopic investigations and obtained partial bandgap energy information in agreement with Hilfiker et al The anisotropic dielectric constant for photon energies far below the bandgap but far above optical phonon mode frequencies were obtained from IR ellipsometry measurements (ε ∞,⊥ =3.75 and ε ∞, =3.64), 26 which agreed reasonably well by extrapolation from the near IR ellipsometry analysis (ε ∞,⊥ = 3.86, ε ∞, = 3.76) and direct Cauchy model analysis (ε ∞,⊥ = 3.864, ε ∞, = 3.756) performed by Hilfiker et al 22,32 Of fundamental importance for device design and operation is precise knowledge of phonon mode properties and static dielectric constants. A complete picture for these properties has not emerged yet.…”

“…All of the TO modes were identified except for the lowest E u mode due to lack of access to the far-IR range. 26,36 Akaiwa et al currently report the highest mobility value achieved for tin-doped alpha phase gallium oxide at 65 cm 2 /(Vs). 41 Sharma and Singisetti predicted a low field isotropic average electron mobility of ≈ 220 cm 2 /(Vs) and suggested polar optical phonon scattering as the dominant limitation for electron density of 1.0 × 10 15 cm −3 .…”

“…Feneberg et al published data calculated by density functional theory (DFT) for all transverse optical (TO) phonon modes (4 modes with E u and 2 modes with A 2u symmetry). 36 Experimental investigations were reported by Feneberg et al using spectroscopic ellipsometry in the IR range. All of the TO modes were identified except for the lowest E u mode due to lack of access to the far-IR range.…”

Reduction of dislocations in α-Ga2O3 epilayers grown by halide vapor-phase epitaxy on a conical frustum-patterned sapphire substrate

“…These characteristics are dominant in -Ga 2 O 3 compared with -Ga 2 O 3 (Neal et al, 2017). In addition, -Ga 2 O 3 has a corundum structure, which forms a ternary system with indium oxide and aluminium oxide, enabling both bandgap engineering to produce a desired wavelength and function engineering to improve the characteristics using transition metals (Cr, Fe, V, Ti) (Feneberg et al, 2018). However, -Ga 2 O 3 undergoes a phase transition at high temperature (>700 C) involving a metastable state, which is an undesirable disadvantage; hence, the substrate cannot be fabricated by liquid-phase growth, and only heteroepitaxy growth occurs (Oshima et al, 2015;.…”