CRYSTALLOGRAPHIC TILTING RESULTING FROM NUCLEATION LIMITED RELAXATION

We have measured the crystallographic tilt in thick relaxed Si0.7Ge0.3 layers grown on vicinal (001) Si substrates, with and without a step graded intermediate layer, as a function of the angle of miscut away from the exact (001) surface. In both cases, the tilt angle has the same azimuthal orientation as the miscut, but is opposite in sign, and varies linearly with the angle of miscut. The tilt is significantly larger for samples with intermediate graded layers, reaching 0.6-degrees for an angle of miscut of 2-degrees. We interpret these data by noting that relaxation of layers grown on top of a compositionally graded buffer occurs by a nucleation limited mechanism, whereas relaxation in samples grown without graded buffers is glide limited. The miscut affects the activation energy of nucleation, which is an exponential effect, while it linearly changes the glide force applied on dislocations.