Implantation damage in GaAs-AlAs superlattices of different layer thickness

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Abstract
We report that two GaAs-AlAs superlattices of different layer thickness show dramatically different crystal damage when ion irradiated under identical conditions. The samples, held at 77 K, were implanted with 100 keV 28Si at doses of 3×1013 cm−2 to 1×1015 cm−2. Ion channeling results show amorphization threshold doses of 1×1015 cm−2 for the 7.0 nm GaAs-8.5 nm AlAs superlattice and 4×1014 cm−2 for the 3.5 nm GaAs-5.0 nm AlAs superlattice. At low doses, the shorter period superlattice was more robust, with no damage peak observed in ion channeling spectra for doses as high as 1×1014 cm−2. For a dose of 7×1013 cm−2, double crystal x-ray diffraction measurements show a 6 arcsec broadening of the (004) peak, relative to that of the unimplanted sample, for both superlattices. However, only the finer period superlattice exhibits a broadening (10 arcsec) of the (224) diffracted peak indicating a distortion in an additional direction. A mechanism involving the formation of slightly misaligned crystal domains is suggested to describe the behavior of the finer period superlattice.