ION-BOMBARDMENT INDUCED RELAXATION OF STRAINED ALGAAS GAAS HETEROSTRUCTURES STUDIED BY THE COMPLEMENTARY USE OF RBS-CHANNELING AND X-RAY SYNCHROTRON-RADIATION/

AlxGa1-xAs epitaxial layers grown on semi-insulating GaAs (SI-GaAs) su bstrates with x = 0.25 and on in-doped GaAs with x = 0.45 were implant ed at room temperature with 1.5 MeV Se ions to fluences ranging from 0 .6 x 10(14) to 4 x 10(14) at/cm(2). Implanted crystals were analyzed w ith 1.8 MeV He-4 ions using the RBS/channeling technique. In order to determine the defect structure and their depth profiles measurements w ere carried out at two different temperatures: 295 and 105 K. XRD with synchrotron beams was used for structural analysis. White beam topogr aphy 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 significant tetragonalization of the implanted region was observed. For the layers grown on SI-GaAs the lattice distortion increases with increasing ion dose until a cri tical lattice strain is attained. Ar that point the complete relaxatio n of the epitaxial layer occurs. In contrast, no relaxation was observ ed for layers grown on practically defect free in-doped substrates. Th e mechanism of this transformation is attributed to the much higher di slocation density in the SI-GaAs substrate. Nucleation of new dislocat ions at defects produced by ion implantation and their interaction wit h threading dislocations leads to the strain relaxation by plastic def ormation of epitaxial layers. (C) 1998 Elsevier Science B.V.