IMPLANTATION DAMAGE IN GAAS-ALAS SUPERLATTICES OF DIFFERENT LAYER THICKNESS

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 Si-28 at doses of 3 X 10(13) cm-2 to 1 X 10(15) cm-2. Ion channeling results show amorphization threshold doses of 1 X 10(15) cm-2 for the 7.0 nm GaAs-8.5 nm AlAs superlattice and 4 X 10(14) 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 X 10(14) cm-2. For a dose of 7 X 10(13) 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.