Electrochemically-Modulated Semiconductor Crystal Growth from Liquid Metal Electrodes.

Abstract

This thesis describes a new electrochemical synthetic strategy for direct growth of crystalline covalent group IV and III–V semiconductor materials at or near ambient temperature conditions. This strategy, which we call “electrochemical liquid–liquid–solid” (ec-LLS) crystal growth, marries the semiconductor solvation properties of liquid metal melts with the utility and simplicity of conventional electrodeposition. A low-temperature liquid metal (i.e., Hg, Ga, or alloy thereof) acts simultaneously as the source of electrons for the heterogeneous reduction of oxidized semiconductor precursors dissolved in an electrolyte as well as the solvent for dissolution of the zero-valent semiconductor. Supersaturation of the semiconductor in the liquid metal triggers eventual crystal nucleation and growth. In this way, the liquid electrolyte–liquid metal–solid crystal phase boundary strongly influences crystal growth.

The intent of this thesis is to summarize the key elements of ec-LLS identified to date, first contextualizing this method with respect to other semiconductor crystal growth methods in Chapter 1 and then highlighting some unique capabilities of ec-LLS in subsequent chapters. Specifically, Chapter 2 describes the first demonstration of an epitaxial ec-LLS growth process of single-crystalline germanium (Ge) nanowires at room temperature in a massively parallel fashion. Chapter 3 further extends the concept of heterogeneous nucleation in ec-LLS into the micron-sized scale regime by describing highly ordered crystalline Ge microwire arrays. Chapter 4 addresses the hypothesis as to whether the liquid metal electrode in ec-LLS can also serve as a reactant source for preparation of the compound semiconductor, GaAs. Chapter 5 demonstrates a new electrochemically-induced alloy formation process to directly prepare crystalline InAs films in aqueous electrolytes at room temperature. And Chapter 6 summarizes and contextualizes the cumulative conclusions of this thesis while describing future research directions.