Temperature-Dependent Anisotropic Refractive Index in β-Ga₂O₃: Application in Interferometric Thermometers

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Accurate optical properties of β-Ga₂O₃ are essential for photonics.
• Temperature dependence of these properties requires further investigation.
• Optical micro- and nanocavities offer diverse applications.

Purpose of the Study:

• Analyze the temperature effect on β-Ga₂O₃'s anisotropic refractive index.
• Investigate thermal shifts in microcavity optical resonances.
• Compare experimental findings with simulations.

Main Methods:

• Ellipsometry on bulk β-Ga₂O₃ to determine temperature-dependent refractive index.
• Sellmeier formalism fitting for dispersion relations.
• Micro-photoluminescence spectroscopy of Cr-doped β-Ga₂O₃ nanowire microcavities.
• Finite-difference time-domain (FDTD) simulations.

Main Results:

• Obtained temperature-dependent, anisotropic refractive index dispersion relations for β-Ga₂O₃.
• Observed characteristic thermal shifts in Fabry-Perot resonances within nanowire microcavities.
• FDTD simulations showed good agreement with experimental μ-PL results, with slight differences attributed to refractive index variations.

Conclusions:

• The study quantifies the thermo-optic coefficient of β-Ga₂O₃.
• Experimental and simulation results confirm the significant impact of temperature on β-Ga₂O₃ microcavity optical resonances.
• Findings are vital for designing temperature-stable β-Ga₂O₃-based photonic devices.