Ph.D Thesis

Ph.D StudentGreenberg Ya'akov
SubjectEpitaxial Growth of Semiconductor Nanowires
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisor PROF. Dan Ritter
Full Thesis textFull thesis text - English Version



Epitaxial semiconductor heterostructures have many applications in electronics and optics. However, epitaxial growth of materials that are not lattice mismatch is limited by defect formation. Due to their small footprint, semiconductor nanowires relieve the lattice-matching requirement, and are ideal for achieving epitaxial growth of mismatched semiconductor layers.

This thesis describes the growth of III-V semiconductor nanowires by the vapor liquid solid method using metal organic molecular beam epitaxy and gold seed particles. Heterostructures having atomically sharp interfaces were achieved. During metal organic molecular beam epitaxy, growth precursors are introduced into an ultra high vacuum chamber. Group III elements are supplied as metalorganic compounds and crack on the surface of the substrate. Group V elements are supplied as hydrides and are pre-cracked in the gas injector. Ordered arrays of nanowires were obtained by positioning the gold seed particle using electron beam lithography. 

This work summarizes the initial steps and subsequent achievements of nanowire technology at the Technion. Growth parameters such are substrate temperature, flow rates, and catalyst preparation, were investigated and optimized. Nanowire properties such as growth rate, tapering, crystal structure, and chemical composition were studied. Nanowires were grown by selective area vapor liquid solid (SA-VLS), in which nanowires are grown from seed particles deposited inside holes in silicon nitride material covering the substrate. Such wires were found to grow as pure wurzite nanowires, diffusion length along wires side facet was found to be dependent on catalyst diameter. Nanowires were also grown from variety of materials such as GaAs. It was discovered that carbontetrabromine doping has a great impact on GaAs nanowire yield and growth rate. Heterostuctures were grown and analyzed, and their interface sharpness, as well as crystal structure purity, were determined. It was discovered that SAVLS method could be used to produce atomically sharp interfaces between adjacent materials in the heterostructure.