Microstructure of Ge/Si superlattices growth at low temperature

Si/Ge superlattices were grown at low temperature with modified Stranski-Krastanov (SK) MBE method. X-ray specular, off-specular reflectivity, and X-ray transverse scattering measurements were done to characterized the structure of the Ge/Si superlattice. The fitted roughness and the thickness of the Ge-layer indicate that Ge may diffuse into Si-layer and form the inverted trapezium or nano-scaled hut at the Si/Ge interface. The inverted trapezium extends to form islands, which can be estimated from the volume of the Ge-Si alloy in the structure. These islands can be averaged as a Ge-Si alloy sub-layer, the averaged thickness was fitted from the pure X-ray specular reflectivity. The composition of Ge in the SiGe dots was estimated as 15%-25% by X-ray specular reflectivity and by the thickness of Ge sub-layer. These results were confirmed by TEM observation