STRAIN RELAXATION IN SI1-XGEX LAYERS ON SI(001)

The lattice relaxation of strained Si1-xGex layers on Si (001) substrates has been examined. Three specimens consisting of a single Si1-xGex layer were grown by molecular beam epitaxy. All layers were grown with a nominal composition of x = 0.14 to thicknesses of 0.5, 1.0 or 1.5-mu-m. Double-crystal and white-radiation topographic methods were used to reveal the misfit dislocation structure and distribution. The misfit dislocations were shown to extend from heterogeneous nucleation sites along the [110] directions in the plane of the interface. A symmetric distribution of dislocations between the orthogonal [110] directions was observed. The Burgers vectors of the misfit dislocation array were evenly distributed amongst the available 60-degrees-type candidates. Double-crystal X-ray diffractometry showed the 0.5 and 1.0-mu-m layers to be fully strained to within the experimental uncertainty. Secondary branching of misfit dislocations was observed in the 1.0-mu-m layer which indicated cross-slip of the threading dislocation segments.