Modelling interdiffusion in epitaxial multilayer structures using X-ray simulation techniques

The analysis of X-ray diffraction data forms an important non-destructive technique for the study of interdiffusion in multilayer structures. A frequently used approach is that of Fleming et al. in which the characteristic X-ray diffraction satellites from a superlattice structure are shown to be related to the corresponding Fourier components of the real space composition modulation. This relationship is derived assuming the strain to be small although the limitations on this parameter are unclear. To clarify this limitation the Fleming technique has been tested for a range of x values, and hence strain, using as examples a series of model multilayer CdTe:Cd_1-xMn_xTe structures. The approach has been to use a simulation technique based on the kinematical theory of X-ray diffraction to model the X-ray rocking curves from a series of structures in which the Mn diffusion profiles had been calculated using a particular value of the diffusion coefficient D. The values of the diffusion coefficient, derived from the diffraction data using the Fleming method, agree with the input D at low x values but differ for high x, high strain, structures and a criterion is suggested for the range of validity of the method.