# Near-Field Imaging of Hybrid Surface Plasmon-Phonon Polaritons on n-GaN Semiconductor

## TL;DR

This paper uses near-field imaging to study hybrid surface plasmon-phonon polaritons on n-GaN, revealing their propagation and decay characteristics.

## Contribution

The study provides new insights into the dispersion and propagation of hybrid polaritons on n-GaN using experimental and numerical methods.

## Key findings

- Hybrid polaritons on n-GaN showed decay lengths up to 30 µm at 920 cm−1 in theory.
- At 570 cm−1, decay distances reached 105 µm theoretically, though limited by microscope constraints.
- Dispersion characteristics were validated through numerical modeling and analytical calculations.

## Abstract

Near-field imaging of the hybrid surface plasmon-phonon polaritons on the n-GaN semiconductor was performed using a scattering scanning near-field optical microscope at the selected frequencies of 920 cm−1 and 570 cm−1. The experimental measurements and numerical modeling data were in good agreement, revealing the large propagation distances on the n-GaN semiconductor and other insights which could be obtained by analyzing the dispersion characteristics of hybrid polaritons. In particular, the decay lengths of polaritons at the excitation frequency of 920 cm−1 were measured to be up to 25 and 30 µm in experiment and theory, respectively. In the case of excitation at the frequency of 570 cm−1, the surface plasmon-phonon polaritons’ decay distances were 25 µm and 105 µm, respectively, noting the limitations of the near-field optical microscope setups used. Dispersion characteristics of the resonant frequency and the damping rate of hybrid polaritons were numerically modeled and compared with the analytical calculations, validating the need for further experiment improvements. The launch conditions for the near-field observation of extraordinary coherence of the surface plasmon-phonon polaritons were also discussed.