Ion bombardment induced relaxation of strained AlGaAs/GaAs heterostructures studied by the complementary use of RBS-channeling and X-ray synchrotron radiation

Al_xGa_1-xAs epitaxial layers grown on semi-insulating GaAs (SI-GaAs) substrates with x=0,25 and on in-doped GaAs with x= 0,45 were implanted at room temperature with 1.5 MeV Se ions to fluences ranging from 0,6x10¹⁴ to 4x10¹⁴ at/cm² . Implanted crystals were analyzed with 1.8 MeV ⁴He ions using the RBS/channeling technique. In order to determine the defect structure and their depth profiles measurements were carried out at two different temperatures: 295 and 105 K. XRD with synchrotron beams was used for structural analysis. White beam topography was used to detect lattice deformation and strain relaxation. The lattice parameters were determined by rocking curve measurements with a monochromatic beam. For all samples a signifcant tetragonalization of the implanted region was observed. For the layers grown on SI-GaAs the lattice distortion increases with increasing ion dose until a critical lattice strain is attained. At that point the complete relaxation of the epitaxial layer occurs. In contrast, no relaxation was observed for layers grown on practically defect free indoped substrates. The mechanism of this transformation is attributed to the much higher dislocation density in the SI-GaAs substrate. Nucleation of new dislocations at defects produced by ion implantation and their interaction with threading dislocations leads to the strain relaxation by plastic
deformation of epitaxial layers.