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 degrees C. The fractional relaxation of the buffers grown between 470 and 550 degrees 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/mu m or 0.69% strain/mu m), 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 [110] toward the [1(1) over bar0$] direction suggesting either a bias in the dislocation types in the boule-grown GaAs, or a bias in the way in which alpha and beta dislocations interact with unintentional substrate miscuts. (C) 1996 American Institute of Physics.