Factors affecting the spatial distribution of the principal midgap donor in semi-insulating gallium arsenide wafers

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Abstract
The spatial distribution of an extrinsic variable across a wafer from a melt-grown crystal can provide clues concerning processes during and following solidification. This has encouraged several recent wafer mapping studies in semi-insulating GaAs: for dislocations, for the midgap native donor known as EL2, and for other flaw-related properties. This paper provides maps for the optically measurable neutral EL2 concentration in wafers from Czochralski-grown GaAs crystals. These figures illustrate comments about the factors believed to influence the magnitude and spatial distribution of that midgap flaw. Those factors include the melt stoichiometry and convection, any post-freezing stress, dislocation climb as plastic relief from such stress, and defect reactions in hot solid GaAs. A full accounting for these factors has been hampered by the continuing lack of a generally accepted atomic-scale model for EL2.