Epitaxial Growth, Processing and Characterization of Semiconductor Nanostructures
Abstract: This thesis deals with the growth, processing and characterization of nano-sized structures, eg., self-assembled quantum dots and nano-wires. Such structures are promising candidates for the realization of nano-scale electronic and optical devices, like for instance single electron transistors, resonant tunneling devices, and single photon emitters. For such purposes, the main focus of this work has been on the controlled growth of self-assembled quantum dots. For epitaxy, which is the fundament of this work, low-pressure metal organic vapor phase epitaxy (MOVPE) and ultra high vacuum chemical vapor deposition (UHV-CVD) were used. The structures grown were composed of III/V materials, and SiGe/Si was used for some experiments. For the first group of structures, fundamental investigations on quantum dot growth enabled in-situ growth of InAs/InP self-assembled quantum dot samples in MOVPE. These studies were carried out on freestanding as well as epitaxially overgrown dots. Topography and photo-luminescence were measured with atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) respectively. InAs/InP low-density quantum dot samples were grown in single or multiple layers, suitable for electrical measurements. These structures were studied by electrical characterization (IV), transmission electron microscopy (TEM), and cross sectional scanning tunneling microscopy (STM). Resonant tunneling through these quantum dots was observed, with peak-to-valley ratios as high as 1300 and negative differential resistance up to a point above the temperature of liquid nitrogen. For the second, more complex, group of structures, patterns on semiconductor surfaces were created, either by electron beam lithography and wet chemical etching, or by the partial overgrowth of electron beam induced carbonaceous material. Spatially ordered growth of III/V and SiGe/Si quantum dots on such patterns was studied by AFM. For the InAs/InP system, conditions were found for which dots could be grown selectively in the patterns by the use of As-P exchange reactions. For the SiGe/Si system, commonly quadruples of islands were observed around each pit. The third group of structures was grown from size selected gold particles, deposited in-house in an aerosol machine, or from Au colloids that were dispersed on the semiconductor surface. These gold particles enabled vapor-liquid-solid (VLS) growth of highly anisotropic one-dimensional structures that were characterized by scanning electron microscopy.
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