Magnetron sputter heteroepitaxy of Si_(1-x)Ge_x/Si(001): the evolution of the cross-hatched surface

摘要

The surface step structure of step graded Si_(1-x)Ge_x buffers was investigated by scanning tunneling microscopy (STM). On pseudomorphically grown samples, single atomic steps were found, with the 2x8 reconstruction indicating Ge segreation. Upon strain relaxation, surface slips and the development of the cross-hatched surface takes place. Here, close to the surface slips, the step structure was found to consist of double height D_A steps. This feature is not simply kinematically driven step bunching but can be attributed to the anisotropic strain field on the surface and to the Ge segregation. Analysis of STM cross-sections were taken to estimate the relaxation of our samples. The obtained values agree well with x-ray measurements. The relaxation is found to depend exponentially on the temperature, as the-oretically expected.