Characterization of nanostructure in Si _1-xGe _x epilayers using x-ray reflectivity and fluorescence techniques

X-ray reflectivity and angular dependence of x-ray fluorescence (ADXRF) techniques are used for nondestructive characterization of nanostructure and interface morphology in a series of Si1-x Gex epilayers grown on Si by molecular-beam epitaxy. The ADXRF method is element specific, well suited for probing the depth profile of Ge in the system without disturbing the integrity of the material structure under study. The layer thickness, interfacial roughness, Ge concentration, lattice parameters, and x-ray optical constants for the entire series have been determined. The results show that the Si1-x Gex epilayers with x values between 0.27 and 0.83 are neither completely pseudomorphic nor fully relaxed. We have thus demonstrated that the reflectivity and ADXRF methods can be used as effective tools for studying various types of nanostructure in alloys.