Symmetrical contours of deep level EL2 in liquid encapsulated Czochralski GaAs

Abstract

We have determined the isoconcentration contours of the deep level EL2 across 3-in.-diam, semi-insulating GaAs crystals grown by the liquid encapsulated Czochralski technique. The contours are essentially fourfold symmetric at the seed end of the crystals. The symmetrical pattern is independent of the melt stoichiometry and the relative direction of crystal and crucible rotation. EL2 distributions in the tail of the same crystals are often of lower symmetry. The results support a native defect model for EL2 in which the formation of the defect is enhanced by stress in the crystal.