Epitaxial Growth, Surface, and Electronic Properties of Unconventional Semiconductors: RE-V/III-V Nanocomposites and Semiconducting Half Heusler Alloys
University of California - Santa Barbara Santa Barbara United States
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This dissertation explores how mod cations to and within a parent zincblende lattice, chemical composition and reduced dimensionality, can be used to engineer materials with functionality beyond that of conventional III-V semiconductors. The first part explores the use of dimensionality to control the electronic properties. Here we examine the growth mechanisms and properties of semimetallic rare earth monopnictide RE-V nanostructures embedded coherently within a semiconducting IIIV matrix. We show that by increasing the Er composition during simultaneous growth with GaSb, a wide range of new nanostructures form. These ErSb nanostructures form simultaneously with the GaSb matrix, and by combining molecular beam epitaxy MBE with in-situ scanning tunneling microscopy STM, we image the growth surfaces one atomic layer at a time and show that the nanostructured composites form via a surface-mediate self-assembly mechanisms that is controlled entirely at the growth front and is not a product of bulk segregation. We measure the momentum k- and spatially- resolved electronic structure of the embedded RE-V nanostructures and show that they remain semimetallic down to their smallest dimensions. The second part focuses on Half Heusler alloys, which are a ternary analogue to the zincblende III-Vs. The Full and Half Heusler alloys are an attractive family of multifunctional materials with tunable electronic and magnetic properties. These include both semiconducting and metallic behavior as well as magnetism, half metallic ferromagnetism, superconductivity, topological insulator behavior, and the shape memory effect. We demonstrate the MBE growth of NiTiSn and CoTiSb. The films are epitaxial, single crystalline, and show semiconducting-like transport properties with higher electron mobilities and lower electron densities than their bulk counterparts. These studies lay the groundwork for future studies on all-Heusler heterostructures.
- Properties of Metals and Alloys
- Atomic and Molecular Physics and Spectroscopy