Use of Selective Area Growth for the Reduction of Threading Dislocation Densitiesin Heteroepitaxy

摘要

The central goal of this project has been the achievement of low defect densityGaAs heteroepitaxy on Si by growing mesas with free side walls. Several approaches were used singly and in combination in attempts to guide misfit dislocations (MDs) to the GaAs mesa edges and minimize threading dislocation (TD) densities. Methods included the use of Si pedestals with concave sidewalls, interposed plastically-soft ZnSe buffer layers, graded-composition InGaAs strained layers and post deposition anneals of the various structures. It was found that, surprisingly, TD densities are hardly reduced by the presence of free sidewalls. Moreover, dislocation interactions during the early stages of growth determined the structure and density of TDs in as-grown films and not thermal mismatch strain during cool down from the growth temperature. It was found that graded-strain layers led to a reduction of dislocation densities by a factor of approximately 15 in films grown over pedestals with convex (111) facetted sidewalls. It was concluded that to obtain minimum TD densities it is imperative to prevent formation of 90 deg MDs during lattice mismatched heteroepitaxial growth. The structure and thermal stability of interfaces between ZnSe and Si:As(100) were also determined. The observed asymmetric organization of dislocations was shown to arise from the formation and propagation of misfit dislocations on vicinal surfaces. Heteroepitaxy, Selective area Growth, GaAs on Si.