The study of amorphous gallium arsenide (GaAs)

Mpatani, Ongeziwe
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GaAs is a widely used semiconductor material when doped with different elements of the periodic table to enhance its properties. Over the years, doping has been well established by ion implantation where the induced defects and/or amorphization influences the desired properties for practical applications. In the present investigation, implantations using argon and silicon ions were carried out on crystalline GaAs (c-GaAs) to create a near-surface amorphous layer (a-GaAs). The project aimed to demonstrate how different energies and doses of implantation affect both the damage profile and thickness of the amorphous layer and in turn determine the elastic constants of c-GaAs and a-GaAs. Surface Brillouin scattering (SBS) was used to determine these elastic constants. SBS is an optical technique that probes the nature of surface acoustic excitations propagating on thin films, multilayered and bulk materials. In opaque materials, such as GaAs, the surface ripple mechanism governs the inelastic scattering of light. The measured frequency of the inelastically scattered light is equal to the frequency of the phonon created or annihilated during scattering. This, combined with momentum conservation determines the phonon wave vector. Additionally, for a specific scattering geometry, this data gives the acoustic velocity of the propagating modes and through the inverse problem approach that is used to estimate the elastic constants of the material. Raman spectroscopy was employed to study materials crystallinity with implantation induced dis order because the Raman line is sensitive to the crystal structure and its changes. Due to this characteristic, the level of amorphization as a result of both energy and dose was traced. This analysis method is mediated by the Raman effect which explains the inelastic interaction of matter with light. Several complimentary techniques were utilized to study how the different implantation conditions affect the physical properties of GaAs. These experimental methods include; X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD) and X-ray reflectivity (XRR). Information such as the density of the un-implanted and implanted samples coupled with the crystallite sizes of the implanted samples were determined.
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science to the Faculty of Science, School of Physics, University of the Witwatersrand, Johannesburg, 2022