Designing and Modelling of Nanostructures for Plasmonically Enhanced Hot-Electron Devices

Abstract

Plasmonically Enhanced Hot-Electron (PEH) devices are a new category of optoelectronic devices based on the excitation of hot electrons over a metal-semiconductor junction. Due to their spectral tunability, PEH devices have attracted interest for applications such as tailored photodetection, solar energy conversion, photocatalysis and water splitting.

The efficiency of PEH devices depends on the absorption of incident photons in metal nanostructures, generation of hot-electrons and collection of them by injection over the Schottky junction. The internal quantum efficiency (IQE) of PEH devices is typically limited to a few percent on resonance. Theoretical work has shown that the rate of hot electron generation is dependent on the size of the metal nanoparticles (NPs). Metal NPs with diameters less than 10 nm have the highest generation rates, which could mitigate the low IQE of hot-electron devices. However, arrays of small NPs have limited absorption, and the resonant wavelength cannot be easily tuned.

In this thesis, I demonstrate optical methods to optimize and control the absorption in small NPs. I design dual-scale plasmonic nanostructures, including large-scale Au gratings that can optimize the absorption and small-scale Au NPs that can increase the generation of hot-electrons in PEH devices. This research aims to demonstrate strong, tunable absorption in Au NPs to enhance the performance of PEH devices. Using 2D optical modelling, I investigate the effect of the coupling between different resonant modes of gratings and localised surface plasmons in Au NPs. I show that the wavelength and strength of the resonances can be tuned in small NPs absorption in the visible and infrared spectral regions. Furthermore, I demonstrate that introducing a dielectric layer between the NPs and the gratings can increase the absorption in the NPs up to 3.8-fold. These preliminary designs are a promising method to increase absorption in small NPs and achieve the tunability in absorption spectra for application in high-efficiency PEH devices in the future.