Polarization-resolved broadband dielectric properties of an undoped β-Ga2O3 (100) crystal in the visible to terahertz regions

Abstract

We investigate broadband dielectric properties of an undoped β-Ga2O3 (100) crystal by polarization-resolved transmission spectroscopy in the visible to terahertz regions. We observe average transmittances higher than 0.80 together with a slight birefringence for wavelengths below 6.0 μm (wavenumbers above 1660 cm−1), polarization-dependent stopbands for 12.5–65.0 μm (800–154 cm−1) indicative of reststrahlen bands, and a substantial birefringence for frequencies of 2.0–0.29 THz (66–9.8 cm−1). We find that the high transparency is a useful property for optical windows, while infrared vibrations responsible for the stopbands are significantly anisotropic and induce the terahertz birefringence.