Date of Completion
Dr. John E. Ayers
Dr. Rajeev Bansal
Dr. David Tonn
Dr. Eric Donkor
Dr. Faquir Jain
Field of Study
Doctor of Philosophy
Metamorphic buffer layers (MBLs) allow tremendous flexibility in designing novel semiconductor heterostructures for application in various microelectronic and optical devices. However, device fabrication, reliability and performance are limited by lattice relaxation mechanisms and dislocation defects that are associated with the growth of mismatched material systems. Therefore, understanding the extent of strain relaxation and dislocation dynamics in semiconducting heterostructures has important implications in the design of devices which exhibit desired strain and dislocation characteristics. In this dissertation, we present equilibrium and plastic flow models which are applicable to multilayered and compositionally-graded semiconductor heterostructures and have studied both the thermal equilibrium and kinetically-limited lattice relaxation; in our work, we have accounted for the time evolution of kinetically-limited and equilibrium strain relaxation, thermal activation of glide, and misfit-threading dislocation interactions.
First, this dissertation reports the equilibrium lattice relaxation of various semiconductor epitaxial heterostructures including the distributions of the residual strain and misfit dislocation (MD) characteristics. Up until recently, equilibrium modeling has been accomplished by complex numerical energy-minimization schemes, which are non-intuitive, require specialized code, and are computationally intense. In order to address these complexities, we have developed an electric circuit model (ECM) approach for the equilibrium analysis of an epitaxial stack, in which each sublayer may be represented by an analogous circuit configuration. This new approach enables analysis using widely accessible circuit simulators, and an intuitive understanding of electric circuits may be translated to the relaxation of strained-layer structures. Furthermore, the ECM allows the development of analytical expressions for the strain, misfit dislocation density, critical layer thickness and widths of MD free zones for a continuously-graded layer having an arbitrary compositional profile.
Second, this dissertation describes the development of novel approaches for controlling the lattice relaxation mechanisms and the generation of dislocation defects based on the equilibrium and plastic flow models. Some of these key approaches include dislocation compensation, strain compensation and combinations of temperature- and compositional-grading for controlling the lattice relaxation rates. For each structure type, we studied the requirements on thickness and compositional profile to remove mobile threading dislocations or tailor the strain.
Kujofsa, Tedi, "Equilibrium and Kinetically-Limited Lattice Relaxation of Multilayered and Compositionally-Graded Semiconductor Metamorphic Heterostructures" (2017). Doctoral Dissertations. 1402.