Probing Active Nanophotonic Materials Phenomena Under Electrostatic Modulation

Citation

Kim, Areum (2024) Probing Active Nanophotonic Materials Phenomena Under Electrostatic Modulation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/16x8-7x89. https://resolver.caltech.edu/CaltechTHESIS:05302024-043707549

Abstract

Nanophotonic metastructured devices have gained significant attention due to their ability to manipulate properties of light such as the wavelength, amplitude, and phase. For photonic metastructures, these properties are typically fixed at the time of fabrication, as they depend on the geometrical parameters of resonant structures. Therefore, there is a growing interest in active nanophotonic devices, which can dynamically control the properties of light by incorporating active materials and applying external stimuli, in operation after fabrication.

This thesis investigates the dynamic control of light through electrostatic modulation of metastructures containing indium tin oxide (ITO) and monolayer transition metal dichalcogenides (1L-TMDs) materials. Specifically, we analyze the dynamic behavior of these materials, characterizing their morphological, electrical, and optical properties within devices.

In the first two chapters, we discuss the effects of ion migration on the electro-optic response of ITO-based active nanophotonic devices. Initially, we investigated uniformly deposited silver/dielectric/ITO heterostructures. Under electrical bias, silver ions and oxygen vacancies in the ITO actively migrate changing the device operating characteristics, resulting in hysteretic current-voltage curve behavior. Although optical modulation was barely observed, we explored the thermodynamic instability giving rise to electrical hysteresis in this volatile device. Furthermore, we investigated the impact of oxygen vacancy ion migration on the frequency response and phase modulation of ITO-based active metasurfaces. By annealing the devices, we were able to reduce the oxygen vacancy concentration, thereby improving the device high frequency performance.

In the latter two chapters, we explore the electro-optic response of field effect heterostructures comprised of 1L-TMDs in high-Q resonators. We designed and simulated two distinct types of high-Q resonators: Fabry-Perot resonators and silicon pillar resonators. We optimized the geometrical parameters of these resonant structures embedded with 1L-TMDs to enhance device amplitude and phase modulation. Subsequently, we examined the potential for electro-optic modulation of TMDs in the telecommunication band, beyond their excitonic resonance wavelengths, by integrating them with Fabry-Perot resonators. We also discussed the compatibility of 1L-TMDs with gated heterostructure fabrication methods.

Overall, this thesis presents the application of electrical bias as a tool for the dynamic control of light in ITO and 1L-TMDs-based nanophotonic devices, with potential future applications in adaptive and reconfigurable photonic technologies.

Thesis Files