We report on the growth and characterization of high-quality strain-relaxed SiGe alloys on a compliant silicon–on–insulator (SOI) substrate. The annealing temperature required for strain transfer has been reduced through boron implantation to the buried oxide, leading to a high quality SiGe alloy free from dislocations as evident from the near-band gap photoluminescence. Nearly complete strain relaxation (∼95%) for SiGe alloy of a thickness beyond the conventional critical thickness has been obtained.

The combination of different X-ray topography techniques and reciprocal space mapping is used to monitor the early stages of relaxation in silicon-based heterostructures. For lightly doped silicon layers grown on heavily boron-doped 150 mm substrates, Lang transmission topography demonstrates that an orthogonal array of 60 • misfits nucleates only at the wafer periphery. The length of the individual misfit segment depends on the epitaxial layer thickness and on the presence of the orthogonal blocking misfit segments. Double-crystal X-ray topography, with better strain and tilt resolution, allows one to distinguish between the different tilt components of parallel misfit dislocations. Relaxation is quantified using triple-axis X-ray diffraction. Reciprocal space maps around both the ( 004) and ( 224) reflections show that the misfits relieve about 38% of the strain. The combination of these X-ray techniques offers insight into the means to reduce dislocation formation and into the fundamental nature of the dislocations themselves.

A method to grow a relaxed Si0.5Ge0.5 graded layer with a very smooth surface and a very low threading dislocation density using solid-source molecular-beam epitaxy is reported. This method included the use of Sb as a surfactant for the growth of a 2 μm compositionally graded SiGe buffer with the Ge concentration linearly graded from 0% to 50% followed by a 0.3 μm constant Si0.5Ge0.5 layer. The substrate temperature was kept at 510 °C during the growth. Both Raman scattering and x-ray diffraction were used to determine the Ge mole fraction and the degree of strain relaxation. Both x-ray reflectivity and atomic force microscopy measurements show a surface root mean square roughness of only 20 Å. The threading dislocation density was determined to be as low as 1.5×104 cm−2 as obtained by the Schimmel etch method. This study shows that the use of a Sb surfactant and low temperature growth is an effective method to fabricate high-quality graded buffer layers.

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