Gallium Metal Nanoparticles for Plasmonics and Droplet Epitaxy: Formation and Properties.

Abstract

The development of new materials in nanophotonics, defined as the use of multiscale materials to control light-matter interactions, has proven to be the foundation for revolutionary advances in both science and technology. In this thesis, we utilize Ga droplets as a plasmonic metal nanoparticle (NP) as well as a seed for droplet epitaxy of ZB GaN nanostructures, and examine the formation of embedded GaAs:Ga nanocomposites and ZB GaN nanostructures, and their structural and optical properties. Metallic nanostructures generate surface plasmons an incident electromagnetic wave, leading to enhancements in absorption and emission. However, materials research and device fabrication have focused nearly exclusively on 2-dimensional dispersions of Ag and Au formed on surfaces, with plasmon resonances limited to visible wavelengths. Thus, it is necessary to explore a new plasmonic materials, which cover wide wavelength ranges. Here, we examined the formation of embedded Ga NP arrays and their influence on GaAs NBE PL efficiency using ion beams and molecular beam epitaxy. Using a combined computational-experimental approach, we revealed new insight into the influence of the embedded NPs on the PL of GaAs. This approach provides an opportunity to enhance the PL efficiency from a variety of semiconductor heterostructures, using a seamless approach to embed non-noble metals during epitaxy. GaN is of interest for optoelectronic applications. However, GaN typically crystallizes in a WZ structure, exhibiting piezoelectric properties leading to a reduced probability for recombination of electrons and holes and consequently limit the performance of devices. Thus, interest in polarization-free ZB GaN nanostructures is rapidly increasing. In this thesis, we first demonstrate the growths of ZB GaN nanostructures via DE. By varying the surface conditions of substrates and nitridation processes, GaN QDs were grown polycrystalline, WZ, and ZB. Furthermore, we examined the growth of ZB-WZ mixed NW growth via controlling SiNx interlayer formation, using a two-step MBE growth method of Ga pre-deposition followed by GaN growth on Si (001). We demonstrate, for the first time, a growth process consisting of pre-deposition at high Ga flux, followed by GaN growth at low Ga flux, thereby resulting in GaN NW ensembles with a significant ZB content.