X-ray-diffraction study of the lattice distortions induced by a fractional monolayer:ZnTe embedded in vicinal CdTe(001)

Abstract

The distortion gradient of the interplanar distances induced by a ZnTe fractional monolayer embedded in vicinal B-type CdTe(001) is analyzed within a kinematical model from the diffuse scattering near the (004) Bragg peak of the substrate (scans along [00l]). It is explained how these x-ray measurements allow us to extract the relevant structural parameters of the sample. With this method, only the planes with distortions along the growth direction and without local bending give a significant contribution to the diffuse scattering along [00l]. The measured diffuse intensity only comes from a fraction of the sample volume. It is shown that the elasticity theory is very well verified in the monolayer limit by comparing the strains predicted by this theory to ab initio pseudopotential calculations. By assuming that this approach is still valid in the submonolayer range, the maximum Zn concentration per plane and the integrated Zn quantity are deduced from the distortion curves. The asymmetric profile of the Zn concentration can be explained by a nucleation of ZnTe islands. This analysis of the diffuse scattering has been proven to be very sensitive to the elastic deformation of the layers due to the large lattice mismatch between CdTe and ZnTe (about 6%), but not to the chemical composition of the cationic planes (Cd or Zn). In a more general way, it can easily be applied to systems having a large chemical contrast.