Optical Characterization of GaAs Nanowires Using Specular Mueller Matrix Ellipsometry

Abstract

The purpose of this thesis is to preform ellipsometric measurements to investigate the possibility of in situ characterization of nanowire growth. This will give an advantage for scientist in the future when growing nanowires both economic and time saving. Since ellipsometry is an accurate non-destructive technique, there are attractive possibilities for characterization of morphology and optical properties, which could lead to improving design of novel electro-optical devices. Seven different samples of nanowires were under investigation using specular Mueller matrix ellipsometry. The nanowires mainly consist of gallium arsenide (GaAs) grown on a Silicon (Si) substrate. Some core-shell structures was also investigated. The ellipsometric measurements have been done on both random and patterned grown nanowires, and characterized for different length and incidence angles. The patterned samples can be considered as photonic crystals, where the azimuthal orientation is displayed. There have previously been created a numerical algorithm to simulate Mie scattering for GaAs nanowires, as well as specular reflectance for an effective medium approximation looking at an ensemble of nanowires. For high density grown nanowires it is possible to detect similarities in behaviour between simulated and measured data for various incidence angles. It is possible to detect relatively high anisotropy in the measured Mueller matrix for the nanowire samples.