Heterogeneous Organic Reactions on Gallium-Rich Gallium Arsenide, Gallium Phosphide, and Gallium Nitride Surfaces.

Abstract

This dissertation details a wet chemical reaction strategy that has been developed to impart chemical and electronic stability, as well as chemical functionality to Ga-rich gallium arsenide (GaAs(111)A), gallium nitride (GaN(0001)), and gallium phosphide (GaP(111)A) surfaces. These materials have a broad range of applications in the fields of sensing, electronics, and photoelectrochemistry. However, the native unprotected surfaces of these materials are highly susceptible to oxidation and chemical attack, which cause deleterious surface states that facilitate charge recombination. Currently, the number of wet chemical routes available for surface passivation is limited. I have demonstrated that the addition of organic groups onto Ga-rich surfaces of GaAs(111)A, GaP(111)A, and GaN(0001) via a two-step chlorination/Grignard reaction sequence effects a surface that is chemically resistant to oxidation in ambient and aqueous environments and has a lower density of electronic defects relative to the native oxide. The Grignard reaction sequence was further used to covalently bind allyl and pentenyl groups, with terminal reactive olefins, to GaP(111)A surfaces. In addition to imparting resistance to oxidation that is comparable with alkyl-terminated GaP(111)A surfaces, covalently bound alkenyl groups allow for further modification of the GaP(111)A surface via secondary reactions. For proof of principle, allyl-terminated GaP(111)A surfaces were secondarily functionalized through Heck cross-coupling metathesis, hydrosilylation and electrophilic addition of bromine reactions. The resultant surfaces were characterized using X-ray photoelectron spectroscopy and grazing-angle attenuated total reflectance Fourier transform infrared spectroscopy. Finally, pentenyl-terminated GaP(111)A surfaces were sequentially modified first through electrophilic addition of bromine and then nucleophilic substitution with sodium azide. The azide-terminated GaP(111)A surface was then functionalized through a Huisgen 1,3 dipolar ‘Click’ reaction with an alkyne derivatized Fe-based molecular catalyst. This wet chemical reaction strategy provides a method to create robust Ga-C surface bonds that impart stability on Ga-rich III-V semiconductor surfaces while also affording chemical functionality that can be leveraged to attach technologically relevant organic molecules to the surface.