Interface morphology in strained layer epitaxy of Si/Si_1-xGe_x layers studied by x-ray scattering under grazing incidence and atomic force microscopy

Abstract

We have studied the interface morphology of a strained and of a relaxed Si1-xGex layer system grown on top of a relaxed Si0.7Ge0.3 buffer on a Si(001) substrate. The strain state of the layers was determined by grazing incidence diffraction (GID). Surfaces have been investigated by atomic force microscopy (AFM) and exhibit anisotropies of RMS roughness and lateral correlation length along the 〈110〉 and 〈100〉 directions, which are parallel and diagonal to the cross-hatch pattern, respectively. Diffuse x-ray scattering under grazing incidence and exit close to the forwards direction revealed conformal roughness of the interfaces at lateral correlation lengths of about 1 μm. To deal with the large RMS roughness of up to 40 angstrom, the concept of interfaces without a lateral cut-off length was used to describe the diffuse x-ray scattering within the Born approximation. In the case of a relaxed layer, additional roughness on a lateral length scale of 30 nm was observed at a buried interface by diffuse scattering out of the plane of incidence.