Realization of Complex III-V Nanoscale Heterostructures

Abstract: Low-dimensional III-V semiconductor nanoscale structures grown by epitaxial processes have emerged as a new class of materials with great promise for various device applications. This thesis describes explorations into the heteroepitaxial growth of III-V semiconductor materials in combination with other III-V materials and in combination with the commonly used Si material, in both thin layer and nanowire geometries. Understanding the heteroepitaxial growth of III-V semiconductor nanoscale structures, and understanding the thermodynamic and kinetic processes involved in the growth of these structures, provides deeper insight into their formation properties. Such understanding also enables highly controlled fabrication of high quality crystal nanostructures composed of these materials, which are of great importance for both advanced physics studies and the next generation of devices. This thesis describes work to explore and understand the heteroepitaxial growth of several promising III-V semiconductor materials, including InAs, GaAs, InP, InSb, and GaSb. The properties of these materials, such as their mobility and their direct band gap, are superior to those of the widely used Si material. The materials have been grown using metalorganic vapor phase epitaxy and molecular beam epitaxy. This thesis describes also the successful epitaxial growth of high quality and thin InAs and GaSb layers on Si substrates, despite the large lattice mismatch between these. It describes also studies of several complex III-V nanowire heterostructures in both axial and radial geometries, such as single axial and double axial InSb-GaSb nanowires in both directions. Moreover, investigation of the radial heteroepitaxial growth of Au-seeded InAs-InP and self-seeded GaAs-GaAsxSb1-x nanowires, which indicated important roles of crystal quality and various surface energies, is described. The combination of two binary materials into a ternary nanowire, apart from scalability, offers the possibility to precisely tune the band gap and carrier mobility for specific applications. Hence, this thesis describes studies into the formation of GaAs-GaAsxSb1-x core-shell nanowires with tuned compositions and into the epitaxial growth of GaxIn1-xSb ternary nanowires for the first time.