Beschreibung:
<jats:p>Equilibrium studies of metamorphic (partially relaxed) buffer layers are important in understanding the strain and misfit dislocation density configurations. The authors present a theoretical study of the equilibrium strain and misfit dislocation density profiles as well as appropriate design equations for nonlinearly graded (logarithmic) buffers for use in accommodating the lattice mismatch of heteroepitaxial InxGa1−xAs/GaAs (001) semiconductor devices. Minimum energy calculations show that the nonlinearly graded profile may be beneficial for the control of defect densities in lattice-mismatched devices because they have several characteristics which enhance the mobility and glide velocities of dislocations, thereby promoting longer misfit segments with relatively few threading arms. This study suggest that the use of nonlinear metamorphic buffer layers are beneficial because they contain (1) a misfit dislocation free zone (MDFZ) adjacent to the interface, which avoids dislocation pinning defects associated with substrate defects, (2) a misfit dislocation free zone near the surface, which reduces pinning interactions near the device layer which will be grown on top, and (3) a large built-in strain in the top MDFZ, which enhances the glide of dislocations to sweep out threading arms. In addition, the authors show that the use of nonlinear compositionally grading may be superior to linearly graded layers depending on the specific application of the heterostructure. Moreover, the use of a nonlinearity coefficient (deviation of the average lattice mismatch) enables comparison of nonlinearly graded metamorphic buffer layers to traditionally grown linearly graded heterostructures. The authors also present approximate design equations for the widths of the misfit dislocation free zones, the built-in strain, and peak misfit dislocation density for the general logarithmically graded semiconductor with diamond or zinc blende crystal structure and (001) orientation, and show that these design equations are in fair agreement with detailed numerical energy minimization calculations.</jats:p>