Evolution of the below-bandgap anisotropic refractive indices and dielectric functions of β-(Al <i>x</i> Ga1 <b>−</b> <i>x</i> )2O3 (0 <b>&lt;</b> x <b>&lt;</b> 0.25) determined by generalized spectroscopic ellipsometry
Abstract
We determine the composition dependence of the below-bandgap anisotropic refractive indices and dielectric functions of β-(AlxGa1−x)2O3 for x up to 25% Al. We use Mueller matrix generalized spectroscopic ellipsometry and investigate a set of high quality single crystalline bulk (x=0%,5%,10%,15%,20%,25%) and thin film (4.6%, 9.7%, 12%, 15%, 16.3%, 21%) samples grown by the Czochralski method and by plasma-assisted molecular beam epitaxy, respectively. Bulk samples with 0.2% silicon doping are cut from ingots with (100) surface and the unintentionally doped thin films samples are grown pseudomorphically on (010) β-Ga2O3. The combination of ellipsometry data from both sample sets permits to fully determine the optical properties of the transparent alloys. We employ a quasi-orthorhombic approach which ignores the very small shear components induced by the monoclinic crystal structure. We also ignore the possibly small effects due to strain within the pseudomorphically grown epitaxial samples. We report indices and dielectric functions for polarization along lattice vectors a, b, and reciprocal lattice vector c⋆. All indices reduce with increasing incorporation of aluminum while the spectral range of transparency increases due to the increase in bandgap energy with composition. We use our results to predict Bragg reflector multilayer structures on b-plane β-(Al0.20Ga0.80)2O3, for use in polarization sensitive narrow-band optical filters in the short wavelength region.
Article Details
Journal Info
Applied Physics Letters
American Institute of Physics
Authors (10)
Preston Sorensen
Department of Electrical and Computer Engineering, University of Nebraska-Lincoln 1 , Lincoln, Nebraska 68588,
Alyssa Mock
Department of Electrical and Computer Engineering, College of Engineering, Applied Science and Technology, Weber State University 2 , Ogden, Utah 88402,
Megan Stokey
Department of Electrical, Computer and Biomedical Engineering, Milwaukee School of Engineering 3 , Milwaukee, Wisconsin 53202,
Ufuk Kilic
Department of Electrical and Computer Engineering, University of Nebraska-Lincoln 1 , Lincoln, Nebraska 68588,
Akhil Mauze
Materials Department, University of California Santa Barbara 4 , Santa Barbara, California 93106,
Yuewei Zhang
Laboratory of Flexible Electronics Technology
James Speck
Materials Department, University of California Santa Barbara 4 , Santa Barbara, California 93106,
Zbigniew Galazka
Leibniz-Institut für Kristallzüchtung (IKZ) 2 , Max-Born-Straße 2, 12489 Berlin,
Vanya Darakchieva
Department of Physics, Chemistry and Biology (IFM)
Mathias Schubert
Department of Electrical and Computer Engineering, University of Nebraska-Lincoln 1 , Lincoln, Nebraska 68588,