Strain analysis at the heterointerfaces of III-V ternary alloys: Ultra-thin gallium arsenide phosphate/gallium arsenide superlattices

The principal objective of this research was to characterize heterointerfaces of III-V ternary alloys consisting of ultra-thin GaAsP/GaAs superlattices grown by Molecular Beam Epitaxial (MBE). The area of application for these materials is in optical devices, operating under the visible and IR spectrum. The characterization of heterointerfaces using high-resolution transmission electron microscopy (HRTEM) is divided into two parts: 1) Strain analysis using advanced methodologies known as phase techniques, and 2) Evaluation of chemical contrast, along with minimization of artifacts on HRTEM images, using the Composition Evaluation by Lattice Fringe Analysis (CELFA) method.;Phase techniques for stain analysis on HRTEM images can be divided into two types: Geometric Phase Analysis (GPA) and Computational Fourier Transform Moire (CFTM) method. This research exploits the CFTM method and deals with demonstration of the Computational Fourier Transform Moire (CFTM) method for strain analysis with monolayer accuracy in terms of theoretical implementation. In addition, experimental results using ultra-thin GaAsP/GaAs superlattices are obtained. The CFTM method has not been previously demonstrated for the strain analysis of ternary alloys using HRTEM.;Characterization of strain information on HRTEM images at heterointerfaces of ternary alloys has limitations due to artifacts from the phase technique used for strain analysis. In particular, small lattice-mismatched systems (f<3%) such as GaAsP/GaAs superlattices pose additional challenges. From the methodology point of view, the phase technique generates error at heterointerfaces due to the leakage effect, and it has been shown that the error dominates for small-strained systems (f<3%) with low image resolution. Hence, this research effort was pursued to overcome the leakage effect at heterointerfaces and to minimize error from the phase technique, allowing quantitative structural analysis. Mask-size optimization to suppress the leakage effect at heterointerfaces was proposed and led to a quantitative value of measured strain at a GaAs 0.86P0.14/GaAs superlattice. A simulation method using MatlabRTM for determining the error of the strain values as we exploit the phase technique was proposed such that we can evaluate the reliability of the phase technique with monolayer accuracy. Finally, minimization of artifacts on HRTEM images was conducted and chemical contrast was investigated using Composition Evaluation by Lattice Fringe Analysis (CELFA).