低温生长的Ge/Si超晶格界面结构的X射线散射研究

低温下用MBE方法生长了Ge/Si超晶格,X射线反射及横向散射研究表明,Ge亚层上下表面的粗糙度呈反对称,下表面大的粗糙度来源于Ge向Si亚层中扩散形成SiGe混合组分结构,这种组分结构可以用一平均成分的SiGe合金层加以拟合,从而使得各亚层均有一个合理的粗糙度,旋转样品进行的X射线散射研究表明,这种SiGe的混合是各向同性的,这与透射电子显微镜的研究结构相一致.

Microstructures of Ge/Si Superlattices Growtn 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 characterize the structure of the Ge/Si superlat-tice. 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.