Contour maps of EL2 deep level in liquid-encapsulated Czochralski GaAs

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Abstract
Contour maps of the EL2 deep level concentration across 3-in.-diam, semi-insulating 〈100〉 GaAs crystals grown by the liquid-encapsulated Czochralski technique were determined by optical profiling. The EL2 patterns at the seed end of the crystals are invariably fourfold symmetric, and correlate with the distribution of dislocations. EL2 distributions at the tail, on the other hand, are often less symmetrical. The contour maps are independent of the melt stoichiometry and relative direction of crystal and crucible rotation. The results indicate that whereas the average EL2 concentration along crystals is controlled by the melt stoichiometry, the 10%–20% concentration variations across crystals result from a second effect possibly related to dislocation climb or dislocation gettering. Implications of the observed EL2 distribution on the uniformity of electrical properties is also discussed.