High-Frequency and Below Bandgap Anisotropic Dielectric Constants in α-(Al_xGa_1-x)₂O₃ (0≤x≤1)

Authors

Matthew Hilfiker, University of Nebraska-LincolnFollow
Ufuk Kilic, University of Nebraska-LincolnFollow
Megan Stokey, University of Nebraska-LincolnFollow
Riena Jinno, Cornell University
Yongjin Cho, Cornell University
Huili Grace Xing, Cornell University
Debdeep Jena, Cornell University
Rafal Korlacki, University of Nebraska-LincolnFollow
Mathias Schubert, University of Nebraska - LincolnFollow

Document Type

Article

Date of this Version

9-2-2021

Citation

Appl. Phys. Lett. 119, 092103 (2021)

DOI: 10.1063/5.0064528

Comments

Published under an exclusive license by AIP Publishing. Used by permission.

Abstract

A Mueller matrix spectroscopic ellipsometry approach was used to investigate the anisotropic dielectric constants of corundum α-(Al_xGa_1-x)₂O₃ thin films in their below bandgap spectral regions. The sample set was epitaxially grown using plasma-assisted molecular beam epitaxy on m-plane sapphire. The spectroscopic ellipsometry measurements were performed at multiple azimuthal angles to resolve the uniaxial dielectric properties. A Cauchy dispersion model was applied, and high-frequency dielectric constants are determined for polarization perpendicular (ε_∞,⟂) and parallel (ε_∞,∥) to the thin film c-axis. The optical birefringence is negative throughout the composition range, and the overall index of refraction substantially decreases upon incorporation of Al. We find small bowing parameters of the high-frequency dielectric constants with b_⟂=0.386 and b_∥=0.307.