Optical spectroscopy studies of ion bombarded gallium arsenide and vanadium carbide thin films

• Main Author: Jakata, Kudakwashe
• Format: Others
• Language: en
• Published: 2018
• Online Access: https://hdl.handle.net/10539/25657

Abstract This thesis gives a report on two projects involving the use of the optical techniques of surface Brillouin scattering and Raman spectroscopy to study thin layered materials. In the first case, the thin layered material is formed from ion bombardment of a semiconductor which results in an amorphous layer on a single crystal substrate. The second case involved the study of the elastic properties of vanadium carbide deposited by RF magnetron sputtering on silicon carbide and silicon substrates. There have been a number of reports on the recrystallization of ion implanted GaAs in which it has been noted that it is not a single step process as observed in Ge and Si. These studies have used ion channelling and Raman spectroscopy techniques to establish that the nature of the damaged gallium arsenide layer depends on the implantation conditions such as substrate temperature, implantation ion energy, and fluence. In the present work, the investigation of the recrystallization of ion implanted GaAs using the two optical spectroscopic techniques of surface Brillouin scattering (SBS) and Raman spectroscopy has been carried out for the first time. Single crystals of (100) gallium arsenide were implanted with 100 keV argon ions at liquid nitrogen temperature using ion fluences of 2 × 1014 ions/cm2 and 1 × 1015 ions/cm2 on samples denoted A and B respectively. Additionally, sample C was also implanted with 100 keV argon ions but at an elevated temperature of 50 oC. Raman spectroscopy and SBS measurements are in good agreement for samples A and B showing recrystallization below 300 oC in both cases. Raman measurements on sample A, implanted at the lowest fluence, showed that before annealing was carried out a completely amorphous layer was not achieved. In the early stages of isochronal annealing on both samples A and B, the transverse optical peak is observed to have higher intensity compared to the longitudinal optical peak. At higher annealing temperatures, the longitudinal peak attains higher intensity. Changes in the Rayleigh surface acoustic wave frequency from SBS measurements on Sample C during isochronal annealing are observed from 100 oC and saturation is obtained at about 450 oC. The Raman results show that recrystallization commences above 450 oC and saturates at about 600 oC implying complete recrystallization of the overlayer. Vanadium carbide is a refractory material known for its high hardness, corrosion resistance, high melting point, and high electrical conductivity. There have been a number of studies on the properties of vanadium carbides of different compositions and structures but to the best of the author’s knowledge, there has never been a study on the elastic properties of the thin deposited films. Thin films of vanadium carbide have been grown using RF magnetron sputtering with varying thicknesses on SiC and Si substrates. Different deposition times were used in order to have films with varying thicknesses. X-ray reflectometry, X-ray diffraction, Rutherford backscattering, and atomic force microscopy, have been used to determine the film characteristics such as thickness, roughness, density, and stoichiometry. Surface Brillouin scattering was then carried out. The SBS results were used together with a least squares fitting approach to determine the elastic constants of the VC films computationally. A Green’s function approach was used to verify the results of the fitting procedure. === EM2018