X-ray reciprocal-space mapping of strain relaxation and tilting in linearly graded InAlAs buffers

The extent of relaxation and orientation of linearly graded InxAl1-xAs (x=0.05–0.25) buffers grown on GaAs were examined using a novel x-ray diffraction reciprocal-space mapping technique (kmap). Samples were grown at temperatures ranging from 370 to 550 °C. The fractional relaxation of the buffers grown between 470 and 550 °C was essentially identical (77%) and symmetric in orthogonal 〈110〉 directions. These buffers are believed to be in equilibrium indicating that the incomplete relaxation is not a kinetic effect. The extent of relaxation was less than that expected for equilibrium relaxation in the absence of dislocation–dislocation interactions indicating that such interactions must be considered to accurately predict the extent of relaxation. The saturation of the relaxation as a function of temperature indicates that at the grading rate used (8% In/μm or 0.69% strain/μm), we are not working in a growth regime where the relaxation is nucleation limited. In addition, all the buffers are slightly tilted with respect to the GaAs substrate about [11̄0] toward the [110] direction suggesting either a bias in the dislocation types in the boule-grown GaAs, or a bias in the way in which α and β dislocations interact with unintentional substrate miscuts.