Determination of the interfacial roughness exponent in rare-earth superlattices

The interfacial roughness in Ho/Y and Ho/Lu superlattices has been studied using high-resolution x-ray diffraction. The transverse width of the superlattice Bragg peaks broadens almost linearly as a function of the component of the reduced wave vector parallel to the growth direction, while the line shape is invariant, and is described by a Lorentzian raised to the power of approximate to 5/2. These results are interpreted as a signature of conformally rough interfaces, and the roughness exponent is determined to be alpha = 0.85 +/- 0.05. It is also shown how alpha may be altered by adjusting the growth conditions.