High temperature x ray diffraction measurements on Ge/Si(001) heterostructures: A study on the residual tensile strain

Ge/Si(001) heterostructures grown by means of ultrahigh vacuum chemical vapor deposition have been investigated by means of variable temperature high resolution x ray diffraction in order to investigate the origin of the residual tensile strain observed in this system. To this purpose, we have simultaneously measured the in-and out-of-plane lattice parameters of the deposited Ge films and of the underlying Si substrate, thus allowing us to directly measure the Ge strain evolution as the epilayer was annealed up to and over the deposition temperature and cooled back to room temperature. We have observed that the tensile strain, resulting from the different Si and Ge thermal expansion coefficient, is partially compensated by the residual compressive heteroepitaxial strain, due to the hardening limit of Ge. This limited the tensile strain observable in these heterostructures to similar to 0.002. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3702443]