Researchers from the University of Granada, CNRS, and the University of Montpellier have made significant strides in the field of mid-infrared (mid-IR) plasmonics, focusing on low-loss epsilon-near-zero (ENZ) modes. Their work, led by Julia Inglés-Cerrillo and her colleagues, explores the unique properties of heavily doped gallium nitride (GaN) thin films on silicon, which exhibit low optical losses and desirable ENZ characteristics up to 3 micrometers (μm).
The team’s research, published in the journal Optica, delves into the plasmonic properties of these GaN thin films. Epsilon-near-zero materials, defined by a real part of the permittivity (ε) close to zero, enable unique light propagation characteristics, including confinement within sub-wavelength regions. However, these materials typically suffer from high optical losses. To mitigate these losses, the researchers aimed to find materials that exhibit both near-zero permittivity and a refractive index (n) less than 1, known as near-zero-index (NZI) materials. When both conditions are met, the resulting region is classified as a low-loss ENZ medium, combining strong light confinement with reduced optical losses.
The study provides the first in-depth experimental demonstration of the plasmonic properties of highly doped GaN thin films on silicon. The researchers extracted optical parameters from their experiments and determined the ENZ and NZI regions, comparing their findings with existing literature. They observed a hybridization of surface plasmon and phonon polaritons due to the large polar character of nitrides. This hybridization was accompanied by a flat-dispersion of the high-energy mode, indicative of its ENZ character.
The practical applications of this research for the energy sector are promising. The integration of GaN-based ENZ materials into infrared photonic technologies could lead to more efficient and compact mid-IR devices. These devices could be used in various energy-related applications, such as sensing and monitoring of greenhouse gases, thermal imaging, and free-space optical communication. Additionally, the unique properties of ENZ materials could enhance the performance of solar cells and other energy conversion devices by improving light trapping and absorption.
In summary, the researchers have established GaN as a viable platform for mid-IR ENZ-based plasmonics, paving the way for its integration into future infrared photonic technologies. Their work offers a significant step forward in the development of low-loss ENZ materials, with potential benefits for the energy sector.
This article is based on research available at arXiv.