UC Santa Barbara

This dissertation explores the growth and the electronic properties of materials with strong spin orbit coupling. Thin films of materials with strong spin-orbit coupling are of interest for their potential applications in spintronics and topological quantum computing. The thin films are grown with molecular beam epitaxy, and their structural and electronic properties are investigated with scanning tunneling microscopy and low temperature electron transport.

The first part of this dissertation will investigate the engineering of the mobility and spin-orbit coupling of high mobility InGaAs quantum wells by digital alloying. The mobility of InGaAs quantum wells is significantly limited by alloy disorder scattering. The effect of digital alloying on the mobility of InGaAs quantum wells is investigated, and digital alloying is found to enable record high electron mobilities for InGaAs quantum wells. This record high mobility is due to a reduction in the alloy disorder scattering. In addition, we demonstrate tuning of the spin-orbit coupling in the InGaAs quantum wells by up to 138 meV\textnormal{\AA} by digital alloying. These results demonstrate the ability of digital alloying to engineer and enhance the properties of ternary quantum wells.

The Fermi-level pinning of various InSb surfaces is studied in the second part of this dissertation. The observed Fermi-level pinning is consistent with a charge neutrality point near the valance band maximum. Sb is found to shift the Fermi-level pinning position towards the conduction band minimum, with the (001) surface becoming under electron accumulation when sufficient Sb is on the surface. In contrast, the (111)B surface is found to be strongly pinned, with only minor changes to the Fermi-level pinning upon Sb deposition. The surface treatment of InSb is found to be important for the Fermi-level pinning position, which can be exploited to tailor the properties of InSb based devices.

The last part of this dissertation focuses on the formation of strain solitons in epitaxial bismuth thin films. Synthesizing ultrathin epitaxial bismuth thin films on nonmetallic substrates has remained a significant challenge. Here, the growth of high quality epitaxial bismuth thin films on an InSb (111)B substrate is demonstrated. In these thin films, the epitaxial strain induced in the bismuth from the substrate is relaxed by strain soliton formation. Strain solitons are topological defects in van der Waals materials that can host novel electronic properties, but have only been observed in exfoliated flakes or freestanding layers on mechanically strained bulk crystals. The first scalable approach towards the generation of strain solitons by epitaxial growth is demonstrated. Evidence of edge state localization within the strain solitons is also observed.