Depth dependent optical and elasto-optical effects of ion implantation studied by time-domain Brillouin scattering
Defects, the origin of disorder, can be introduced into a specimen in various ways, e.g. during either materials growth, device fabrication processes or operation in harsh environments. Determining specifics of the relationship between structural disorder and basic optical properties, such as the complex refractive index and the photoelastic coefficients, is the key to understand the behavior of materials that have some amount of disorder. In this thesis, time domain Brillouin scattering (TDBS) is applied to study depth dependent optical and elasto-optical effects of hydrogen ion implantation in silicon carbide and gallium arsenide. TDBS is also further developed for measurements of acoustic deformation potentials as a function of energy. For 4H-SiC the depth dependent modification of optical constants is reported. The results show a strong dependence of the 4H-SiC complex refractive index depth profile on H+ fluence. These studies provide basic insight into the dependence of optical properties of 4H-SiC on defect densities created by ion implantation, which is of relevance to the fabrication of SiC-based photonic and optoelectronic devices. For GaAs, the depth dependent photoelastic coefficient P12 profile arising from H+ implantation is presented. The depth-dependent profile is found to be broader than the defect distribution profile predicted by Monte Carlo simulations. This fact indicates that the changes in photoelastic coefficient P12 depend nonlinearly on the defect concentrations created by the hydrogen implantation. These studies provide insight into the spatial extent to which defects influence photoelastic properties of GaAs.