The Role of Optical Phonon Confinement in The Infrared Dielectric Response of III-V Superlattices

Abstract
Polar dielectrics are key materials of interest for infrared (IR) nanophotonic applications due to their ability to host phonon-polaritons (PhPs) that allow for low-loss, subdiffractional control of light. The properties of phonon-polaritons are limited by the characteristics of optical phonons, which are nominally fixed for most “bulk” materials. Superlattices composed of alternating atomically-thin materials offer control over crystal anisotropy through changes in composition, optical phonon confinement, and the emergence of new modes. In particular, the modified optical phonons in superlattices offer the potential for so-called crystalline hybrids whose IR properties cannot be described as a simple mixture of the bulk constituents. To date, however, studies have primarily focused on identifying the presence of new or modified optical phonon modes rather than assessing their impact on the IR response. This study focuses on assessing the impact of confined optical phonon modes on the hybrid IR dielectric function in superlattices of GaSb and AlSb. Using a combination of first principles theory, Raman, FTIR, and spectroscopic ellipsometry, the hybrid dielectric function is found to track with the confinement of optical phonons, leading to optical phonon spectral shifts of up to 20 cm−1. These results provide an alternative pathway towards designer IR optical materials.
Description
This is the peer reviewed version of the following article: Matson, J. R., Alam, M. N., Varnavides, G., Sohr, P., Knight, S., Darakchieva, V., Stokey, M., Schubert, M., Said, A., Beechem, T., Narang, P., Law, S., Caldwell, J. D., The Role of Optical Phonon Confinement in The Infrared Dielectric Response of III-V Superlattices. Adv. Mater. 2023, 2305106. https://doi.org/10.1002/adma.202305106, which has been published in final form at https://doi.org/10.1002/adma.202305106. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited. This article is protected by copyright. All rights reserved. This article will be embargoed until 12/01/2024.© 2023 Wiley-VCH GmbH
Keywords
confinement, infrared, phonons, spectroscopy
Citation
Matson, J. R., Alam, M. N., Varnavides, G., Sohr, P., Knight, S., Darakchieva, V., Stokey, M., Schubert, M., Said, A., Beechem, T., Narang, P., Law, S., Caldwell, J. D., The Role of Optical Phonon Confinement in The Infrared Dielectric Response of III-V Superlattices. Adv. Mater. 2023, 2305106. https://doi.org/10.1002/adma.202305106