Correlation between defects, residual strain and morphology in continuously graded InGaAs/GaAs buffers

The influence of different types of grading (linear, parabolic and square-root) and growth conditions on residual strain, Threading Dislocation (TD) density, Misfit Dislocation (MD) confinement and surface morphology of MBE grown InGaAs/GaAs buffer layers has been studied by TEM, RES, SIMS and AFM techniques. Non-linear buffers have wider MD-free surface regions and higher MD concentrations near the substrate where the compositional gradients are higher. Lowering the growth temperature and using an As-2 beam leads to symmetric and smoother cross-hatch morphology and removes asymmetries in the residual strain.