Editorial Feature

Exploring the Thermal Tunability of Semiconductor Metasurfaces

Despite the recent incorporation of metasurfaces into a wide range of dielectric applications (some of which include axicon lenses, sub-diffraction focusing devices, beam deflectors and converters, holograms, and antireflection coatings), they are often limited to a specified bandwidth of operation. To further expand on the potential use of metasurfaces, it is imperative that their functionality magnifies their activity and reconfigurability.

To this end, a 2019 Nanophotonics paper examined the role of thermal tunability in metasurfaces, and how knowledge on these properties could expand the tunability and reconfigurable functions of metadevices.

ImageForArticle_17782_15530089168879551.jpg

Science Photo/Shutterstock

Thermo-Optic (TO) Tunability and Reconfigurable Metadevices

One of the main challenges that researchers have faced in attempting to reconfigure metasurfaces is the ability to obtain large and continuous modulations to the optical properties of these planar optical structures; within both subwavelength and low-Q meta-atom resonators. Several different approaches have looked into the potential of several techniques, including ultrafast free-carrier injection, coupling active tuning to liquid crystals, and MEMS, to confront this challenge.

Despite these attempts, no viable solution to fully reconfigure metasurface devices has been achieved. The current study investigated the thermal-optic (TO) effects of high-index silicon (Si) and germanium (Ge) semiconductor resonators over a large temperature range, in an effort to elucidate any available reconfigurable properties.

Methodology

Both the Si and Ge resonators used in this study were spherical and fabricated by femtosecond laser ablation. To characterize the optical properties of both metasurface devices, single particle spectroscopy was conducted at various temperatures, using a Fourier-transform infrared spectroscopy (FTIR) device that was coupled to an infrared microscope.

The thermal tuning capabilities of both the Si and Ge single resonators and their metasurfaces were examined over a temperature range of 80 to 873 Kelvin (K).

Results

The University of California researchers found that by modifying the traditional TO effect, a temperature-dependent resonance frequency shift occurred. Furthermore, at both low and intermediate temperatures, the researchers discovered that all resonances exhibited a red-shift, which followed a normal positive thermo-optic coefficient.

When exposed to higher temperatures and longer wavelengths, the thermal excitation of the free carriers (FCs) were found to exhibit significant bandgap shrinkage, which ultimately caused the TOC value to become negative and yield a dn/dT value that was less than 0. This transition is believed to result from a continuous change in the resonance shift from red-shift at the low and moderate temperature to a blue-shift at the higher temperatures.

Conclusion

By discovering the significant TOC that exists at short near-infrared (NIR) wavelengths within the Si resonators, the researchers of this study identified both amplitude modulators and tunable metafilters that exist at the Si metasurfaces. This discovery highlights the thermally reconfigurable functionality that exists within Si metasurfaces.

As a result, the research discussed here provides an opportunity for semiconductor engineers to continue to investigate the thermally tunable properties of semiconductor metasurfaces in order to one day develop high-Q reconfigurable metadevices.

References

  1. Lewi, T., Butakov, N. A., & Schuller, J. A. (2019). Thermal tuning capabilities of semiconductor metasurface resonators. Nanophotonics 8(2); 331-338. DOI: 10.1515/nanoph-2018-0178.

The research discussed in this article was conducted by researchers from the Department of Electrical and Computer Engineering at the University of California Santa Barbara. This work was also supported by the Air Force Office of Scientific Research and the University of California Office of the President Multi-campus Research Programs and Initiatives.

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Benedette Cuffari

Written by

Benedette Cuffari

After completing her Bachelor of Science in Toxicology with two minors in Spanish and Chemistry in 2016, Benedette continued her studies to complete her Master of Science in Toxicology in May of 2018. During graduate school, Benedette investigated the dermatotoxicity of mechlorethamine and bendamustine; two nitrogen mustard alkylating agents that are used in anticancer therapy.

Citations

Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Cuffari, Benedette. (2019, March 20). Exploring the Thermal Tunability of Semiconductor Metasurfaces. AZoM. Retrieved on April 18, 2021 from https://www.azom.com/article.aspx?ArticleID=17782.

  • MLA

    Cuffari, Benedette. "Exploring the Thermal Tunability of Semiconductor Metasurfaces". AZoM. 18 April 2021. <https://www.azom.com/article.aspx?ArticleID=17782>.

  • Chicago

    Cuffari, Benedette. "Exploring the Thermal Tunability of Semiconductor Metasurfaces". AZoM. https://www.azom.com/article.aspx?ArticleID=17782. (accessed April 18, 2021).

  • Harvard

    Cuffari, Benedette. 2019. Exploring the Thermal Tunability of Semiconductor Metasurfaces. AZoM, viewed 18 April 2021, https://www.azom.com/article.aspx?ArticleID=17782.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback
Submit