Lattice and continuum theories of Huang scattering

The predicted x-ray and neutron scattering by random semiconductor alloys with the zinc-blende structure has been analysed using direct simulation of the scattering from the atoms in the lattice, and also using a continuum theory. This initial work focuses on the special case of the single-impurity limit (small concentration x) where the elastic properties of both of the pure crystals (x = 0 and x = 1) are isotropic and the same. The influence of different atomic scattering amplitudes on the intensity has also been analysed. Distortions occur in the crystal caused by the size mismatch of the impurity atoms, which results in diffuse scattering of which the most important component is the Huang scattering around the Bragg peaks. The Huang scattering has the shape of a double drop and we obtain surprisingly good agreement between the continuum and lattice approaches. This is because long-wavelength concentration waves make the dominant contribution to the divergent Huang scattering, with the remainder of the diffuse scattering being very weak. We have also analysed the influence of elastic anisotropy on the diffuse scattering.