X-ray scattering from dislocation arrays in GaSb

The structure of GaSb layers grown epitaxially on GaAs(001) substrates has been studied by high-resolution x-ray diffraction. The samples with thicknesses between 95 and 2845 Angstrom were grown in Oxford by metal-organic vapour phase epitaxy. The large lattice mismatch is largely relaxed by two intersecting regular arrays of 90degrees dislocations along the [110] and [1 (1) over bar0] directions. The density of the dislocations changes with the thickness but the dislocations remain localized at the interface and both the GaSb layers and GaAs substrates are distorted. The spacing between the dislocations in both the [110] and [1 (1) over bar0] directions decreases while the relaxation increases as the layer thickness increases. We have found the spacing of the dislocations, relaxation and residual in-plane strain along the [110] and [1 (1) over bar0] directions and showed a strong asymmetry in dislocation spacing and relaxation between the two directions. This is because adjacent {110} planes in the zincblende structure are not equivalent as discussed by Abrahams and Buiocchi. Due to. this asymmetry the structure of the GaSb layers is orthorhombic. Scattering from the thinner, less than or similar to450 Angstrom, layers shows that the GaSb grows in islands first and their size and distribution is different along the [110] and [1 (1) over bar0] directions. The 60degrees dislocations in this system only appear in thick, greater than or similar to1200 Angstrom, layers and their density is significantly higher along the [110] direction. The results show the power of high-resolution x-ray diffraction for studying non-destructively growth, relaxation and dislocation structure of thin films and for providing detailed quantitative information about the distortions caused by misfit dislocations in epitaxial layers.