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The molecular beam epitaxial growth of strained InGaAs films grown on GaAs(100) substrates has been studied using in situ reflection high-energy electron diffraction (RHEED). Both the intensity, shape and position of the diffracted beams were monitored during growth. Growth was found to be layer-by-layer up to a strain dependent thickness, at which point three-dimensional clusters were formed. These clusters exhibited (114) facets and were elongated in the  direction. The onset of 3D cluster formation was simultaneous with measurable lattice relaxation. The relaxation was determined using electromagnetic deflection of the RHEED pattern across two detectors. With this arrangement, the lattice constant could be measured to within 0.003Å. The onset could be delayed by lowering the growth temperature. For misfit strain greater than about 2%, the onset occurs at thicknesses less than the Matthews-Blakeslee critical thickness. For smaller strains, the onset occurs at larger thicknesses.
Reflection high energy electron diffraction (RHEED) measurements indicate that the adsorption of As on misoriented Si(100) surfaces drives a multilayer step transition. We find that the formation of multilayer steps is a strong function of substrate temperature and As pressure. Monolayer steps are metastable at low substrate temperature or As pressure. The subsequent nucleation and growth of GaAs by molecular beam epitaxy (MBE) is controlled by the initial Si step distribution. Single domain GaAs grown on the monolayer stepped substrate has Ga terminated steps. Conversely, single domain GaAs grown on the multilayer stepped substrate has As terminated steps.
Mechanisms and phenomena of strain relaxation at bi-material interfaces have been studied for over half a century. The details, however, and limiting kinetics, thermodynamics and mechanics are still being sorted out - particularly for large misfit systems. Three techniques are required to accurately portray strain distributions during and after epitaxial growth: RHEED, TEM and SACP. Reflection high energy electron diffraction (RHEED) is used to measure the lattice parameter during growth. Both transmission electron microscopy (TEM) and selected area electron channeling pattern (SACP) analysis are necessary to identify the defects and the strain distribution. These techniques have been applied to NiAl and FeAl grown by MBE on GaAs with a thin AlAs buffer layer. It is shown that both island and layer by layer growth can occur with the corresponding defects being remarkably similar in character. From a combined Moiré, HREM and computer simulation, the dislocation character is assessed. Both <100> dislocations from half-loops or island edges may occur providing only partial relaxation of the film-substrate systems. The impact of the remaining elastic strain distribution on kinetic measurements of dislocation velocities is discussed.
In this study, transmission electron microscopy (TEM) was used to investigate the growthconditions which produce the highest quality GaAs(111)B films by molecular beam epitaxy (MBE). Low-temperature growth using both As4 and arsine as an As2 source produced highly twinned structures, although the use of As4 provided for a smoother surface and slightly different defect structure. Two distinct twin boundaries, (112)A and (112)B, were identified by cross-sectional transmission electron microscopy (XTEM). The (112)A defect could be over-grown by a subsequent high temperature growth but the roughness associated with the (112)B defects only increased with further growth. High temperature growth of GaAs and AlAs films, while maintaining the GaAs(11)surface reconstruction, resulted in substantial reduction in the number of twins boundaries. We also found that GaAs(111)B layer quality and surface morphology can be further improved by a high temperature growth with low arsenic to Ga flux ratio of I to 1.5 ona slightly misoriented substrate.
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