High quality strain-relaxed thin SiGe virtual substrates have been achieved by combining the misfit strain technique and the point defect technique. The point defects were first injected into the coherently strained SiGe layer through the "inserted Si layer" by argon ion implantation. After thermal annealing, an intermediate SiGe layer was grown with a strained Si cap layer. The inserted Si layer in the SiGe film serves as the source of the misfit strain and prevents the threading dislocations from propagating into the next epitaxial layer. A strained-Si/SiGe/inserted-Si/SiGe heterostructure was achieved with a threading dislocation density of 1×10⁴ cm^-2 and a root mean square surface roughness of 0.87 nm. This combined method can effectively fabricate device-quality SiGe virtual substrates with a low threading dislocation density and a smooth surface.

The paper describes the growth of a germanium (Ge) film on a thin relaxed Ge-rich SiGe buffer. The thin Ge-rich SiGe buffer layer was achieved through a combination of ultrahigh vacuum chemical vapor deposition (UHVCVD) SiGe epitaxial growth and SiGe oxidation. A lower Ge content strained SiGe layer was first grown on the Si (001) substrate and then the Ge mole fraction was increased by oxidation. After removal of the surface oxide, a higher Ge content SiGe layer was grown and oxidized again. The Ge mole fraction was increased to 0.8 in the 50 nm thick SiGe layer. Finally a 150 nm thick pure Ge film was grown on the SiGe buffer layer using the UHVCVD system. This technique produces a much thinner buffer than the conventional compositionally graded relaxed SiGe method with the same order of magnitude threading dislocation density.