Strain-induced abnormal Ge/Si inter-diffusion during hetero-epitaxy process

In this work, strain-induced abnormal inter-diffusion at Ge/Si interface during the hetero-epitaxy process is reported. By mediating the residual strain in Ge epitaxial layer, we reveal an anisotropic inter-diffusion phenomenon during conventional two-step growth process of Ge film. The diffusion length of Ge in Si substrate is found to greatly exceed the theoretical value derived from generalized diffusion model, indicating that the inter-diffusion at the interface is considerably enhanced by the residual strain at growth temperature of 600 degrees C. The diffusion profiles are {111}-faceted, and a rather abrupt diffusion-front is pictured implying that the Fick's law becomes invalid during the inter-diffusion process. Extensive 60 degrees mixed dislocation and stacking faults (SFs) are identified at the diffusion front signifying that the slip of {111} lattice plane is favored at the diffusion front. The net increase of inter-diffusivity at the Ge/Si interface is ascribed to the slip of {111} lattice plane and the preferential diffusion along the dislocation segments, both of which allow the Ge(Si) atoms to migrate across the diffusion front more easily. The findings in this study may cast light on the formation of micro-roughness at interface of Ge/Si hetero-structures during the epitaxy process.