| This dissertation examines stress creation and relaxation processes associated with microstructural evolution during thin film deposition. Three materials systems were examined in this study; GaN on sapphire, AlGaN/GaN heterostructures, and Volmer-Weber films on amorphous substrates. In all three systems the stress during deposition was measured in situ in real-time, and the data was correlated with multiple ex situ analysis techniques.; In the system GaN on sapphire, this work provided the first direct measure of the stress during metal organic chemical vapor deposition of GaN. It was determined that GaN films grew in tension during deposition, despite the compressive lattice mismatch with the sapphire substrate. A model based on the reduction of free volume associated with dislocation annihilation is presented that best accounts for the observed tensile stress.; These studies of lattice-mismatched AlGaN/GaN epitaxial heterostructures focused on the energetics and kinetics of stress relaxation processes. It was determined that AlGaN on GaN relaxed via a combined brittle-ductile mode. The energetics of the stress relaxation was dictated by brittle failure since slip in AlGaN is very difficult. Evidence is presented that suggests that the localized shear stress concentrations around the crack tips promoted introduction of misfit dislocations within the AlGaN/GaN interface.; The stress evolution in Volmer-Weber thin films deposited on amorphous substrates was also studied. This work focuses on Ag, Al, Ti, amorphous Si, and amorphous Ge thin films deposited on the native oxide of Si, which all displayed qualitatively similar stress evolution. The dynamic competition between stress generation due to island coalescence and capillarity, and stress relaxation due to Coble creep, interfacial sheer, and dewetting, was examined in detail. It was determined that interfacial shear dominates relaxation of weakly adherent Ag films, while relaxation in strongly adherent Al films under similar conditions is much slower. Appreciable relaxation occurred only prior to film continuity; after continuity relaxation essentially ceases, a behavior that is consistent with interfacial shear. No stress relaxation was observed in amorphous Ge films deposited at room temperature, which makes this system an ideal candidate for quantitatively studying stress generation free of relaxation effects. |
