Instituto de Óptica “Daza de Valdés”

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

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

Laser Processing Group (LPG)

  • Anisotropic index of refraction implies that the material exhibits different refractive index values in different directions of propagation of light.

Madrid / July 4, 2023

An international study led by the UCM nanomaterials physics group in which the Laser Processing Group of the IO-CSIC has participated has investigated the variations with temperature of the anisotropic refractive index in β-Ga2O3 for its application in interferometric nano-thermometers. The results of this study have been published in the prestigious scientific journal Nanomaterials.

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β-Ga2O3, also known as gallium oxide, has exceptional optical and electronic properties, making it a very interesting material for various applications, including photonics. With its ultra-wide bandgap, which is useful for high-power devices or solar energy conversion, high critical electric field (amount of electric field that an insulator can withstand), thermal stability, chemical resistance, and radiation resistance, it is considered one of the most promising semiconductors for high power devices. Furthermore, β-Ga2O3 can emit light when doped with optically active impurities, making it attractive for luminescent devices.
A light source on a dark background from the front forms a luminous cross
To study variations with temperature the research team focused on the optical micro- and nanocavities that can be created within microwires and nanowires and used them as distributed Bragg reflectors. Bragg reflectors consist of periodic patterns of materials with such a refractive index that they only reflect one wavelength and are very sensitive to variations.
By analyzing the effect of temperature on the anisotropic refractive index of β-Ga2O3, the researchers obtained temperature-dependent dispersion relations using ellipsometry that was performed in the laboratories of the Institute of Optics.

To validate their experimental results, the researchers performed finite difference time domain (FDTD) simulations considering the exact morphology of the wires and the temperature-dependent anisotropic refractive index. The changes caused by the temperature variations observed in the experiments were similar to those obtained with the theoretical calculations, although slightly higher when implementing the refractive index obtained through ellipsometry.

This study provides valuable insights into the temperature-dependent behavior of the anisotropic refractive index in β-Ga2O3 and its impact on high-precision interferometric thermometers.

In addition, the results of this study open up new possibilities for using β-Ga2O3 in various photonic applications, such as sunlight-blind ultraviolet photodetectors for fire detection. /flames and new tunable luminescent devices.

This is a collaborative work between the Department of Physics of Materials of the Complutense University of Madrid, the Laser Processing Group of the IO-CSIC, the Department of Physics of the University of the Basque Country and the Group of Crystals and Semiconductors of the Washington State University.

IO-CSIC Communication
cultura.io@io.cfmac.csic.es

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