Heterostructure SiGe layers on (001)Si substrates, with degrees of relaxation that ranged from nearly pseudomorphic to nearly relaxed, were characterized by means of diffuse X-ray scattering measurements. The lattice constants, Ge content, relaxation, and misfit dislocation density were determined by means of single-crystal diffractometry. The thickness of the SiGe layers was measured, in the as-grown state, by using double-crystal diffractometry. A standard triple-crystal X-ray diffractometer was used to analyze the diffuse X-ray scattering intensity by rotating the analyzer crystal for a fixed sample position. The intensities around the (004) reciprocal lattice point of the substrate were measured by using a wide range of rotation angles for the analyzer crystal. It was found that the diffuse scattering increased steeply, with increasing dislocation density, up to a critical value of 5 x 104/cm. It then saturated, and decreased slowly as the dislocation density increased. This behavior could be explained by superposing the strain fields of neighboring dislocations, above a critical density, so that only heavily distorted regions near to the dislocation core participated in scattering. It was shown that the diffuse scattering technique was a very sensitive tool for detecting relaxation at dislocation densities of less than 5 x 104/cm; whereas diffractometric techniques which monitored lattice constants were near to their resolution limits.

G.Bhagavannarayana, P.Zaumseil: Journal of Applied Physics, 1997, 82[3], 1172-7