X-ray imaging and diffraction study of strain relaxation in MBE grown SiGe/Si layers

Molecular Beam Epitaxy (MBE) grown, 50-800 nm thick SiGe layers on Si are studied by two X-ray complementary techniques: imaging (X-ray topography) and High Resolution X-Ray Diffraction. The measured relaxation rates are spreding from as low as 0.01% to over 70%. These results are examined through the main models for critical thickness t(c) calculation, the Matthews and Blakeslee approach concerning misfit dislocations (MD) development from existing dislocations and the People and Bean model for homogeneous MD nucleation. The beginning step of the relaxation is found to fit exactly with the People and Bean model, otherwise larger relaxation is reached after an intermediate weak relaxation stage. This leads to a refined approach of the critical thickness: a critical band [t(cinf), t(cup)] Comparison between observed t(cexp) and calculated t(c) indicates that the lower limit of this band can be predicted by equilibrium models, the upper one being linked with multiplication stages. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim