The use of Raman spectroscopy to characterize strain in strained Si and strained SiGe has been widely accepted. To use Raman spectroscopy for quantitative biaxial strain measurements, the strain shift coefficient for Si-Si vibration from strained Si (b StSi Si{Si ) and strained SiGe (b StSiGe Si{Si ) must be known. So far, b StSiGe Si{Si is commonly used to calculate strain in strained Si, which may result in inaccurate strain values. In this work, we report the first direct measurement of b StSi Si{Si by correlating highresolution X-ray diffraction and Raman spectroscopy, which yields a measured value of À784 AE 4 cm À1 . We also show that the strain shift coefficient of SiGe, b StSiGe Si{Si , is a strong function of Ge concentration (x), and follows the empirical relation: b ¼ À773:9 À 897:7x for x < 0:35.

We report on the channel strain relaxation in transistors with embedded silicon germanium layer selectively grown in source and drain areas on recessed Si͑001͒. Nanobeam electron diffraction is used to characterize the local strain in the device channel. Our results show that strain is reduced in the device channel regions after implantation and thermal anneal.

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We demonstrate an approach for fabricating relaxed SiGe layers on Si substrate with low threading dislocation density using commercially available low-pressure chemical vapor deposition epitaxy systems. This approach involves a thin epitaxial buffer layer with a reversed Ge composition gradient, i.e., the Ge composition decreases from the Si substrate to the growing surface. On a 90 nm thick buffer, growth of SiGe layer with composition up to 32% Ge was demonstrated with a strain relaxation Ͼ80% and a threading dislocation density below 10 6 cm Ϫ2 .