Abstract
Extensive microstructural characterization of undoped and isovalent (indium) doped, large diameter, semi-insulating GaAs crystals grown in a low gradient LEC configuration has been conducted. As indium is added to GaAs, a dramatic transition occurs in dislocation microstructure from cellular to axial at an indium concentration corresponding to the onset of “lattice hardening”. Both continuous and discontinuous axial dislocations were identified. Characterization of crystals grown with lattice matched seeds, different crystallographic orientations, fully encapsulated melts, and necked seeds showed that reproducible growth of completely dislocation-free crystals remains as a formidable challenge. A model is proposed explaining the nucleation and propagation of axial dislocations in terms of radial inhomogeneities of the indium concentration at the growth interface. Approaches to achieving dislocation-free growth are presented based on this model. Finally, the correlation between dislocation and the EL2 defect center was found to follow the behavior previously reported for undoped material.
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