In situ transmission electron microscopy studies of dislocation/defect interactions in silicon germanium/silicon heterostructures.

摘要

A crucial component in the successful application of strained layer heterostructures in electronic devices is a fundamental understanding of the misfit strain relaxation process. One of the central parameters governing the relaxation process is the kinetics of misfit dislocation generation during both the growth and annealing cycles. In this dissertation, in-situ transmission electron microscopy is used to determine the interaction of propagating misfit dislocations with defects in these structures. Because the specimen geometry and epilayer strain can be well characterized and controlled, it is possible to observe small changes in dislocation motion. This allows quantitative characterization of the fundamental nature of the interaction of moving dislocations with point, line and surface defects in this materials system.; Utilizing the unique capabilities of a specially constructed UHV-TEM equipped with in-situ UHV-CVD growth facilities I have directly measured the propagation velocities of misfit dislocations both during heteroepitaxial growth and during post-growth annealing. It was observed that dislocations continue to propagate at nearly the same velocity during post-growth UHV annealing as they do during growth itself. Following the formation of a thin native oxide layer, dislocation motion is dramatically enhanced. Low energy electron microscopy observations as well as arsenic adsorption experiments indicate that there is an interaction between moving dislocations and the surface reconstruction in this system which slows dislocation motion. Finite element modeling is used to show that the observed increase is most likely a result of stress effects on dislocation kink nucleation at steps along the native oxide - epilayer interface.; Observations of dislocation - dislocation interactions during both growth and annealing of SiGe heterostructures have allowed determination of the range of epilayer thickness and composition where existing interfacial dislocations can exert sufficient force on moving dislocations to halt their motion. The findings have important ramifications on the creation of low dislocation density structures.; Post-growth in-situ annealing of ion-implanted Si/SiGe/Si (001) heterostructures permits observation of the interaction of misfit dislocations with point defects. Implantation of boron directly within the SiGe epilayer results in significantly enhanced dislocation nucleation and overall strain relaxation, but dislocation motion is observed to be impeded by clusters of implantation related defects.; Throughout this dissertation, emphasis is placed on the requirements for accurate quantitative measurements of dislocation motion in this system. These quantitative measurements yield insight into both the fundamental behavior of dislocations in semiconductor materials and into the technologically important process of strain relaxation in semiconductor heterostructures. (Abstract shortened by UMI.)