The predicted x-ray and neutron scattering by random semiconductor alloys A
(1-x)B(x)C with the zinc-blende structure has been analysed using direct si
mulation 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 sing
le-impurity limit (small concentration x) where the elastic properties of b
oth 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 al
so been analysed. Distortions occur in the crystal caused by the size misma
tch of the impurity atoms, which results in diffuse scattering of which the
most important component is the Huang scattering around the Bragg peaks. T
he Huang scattering has the shape of a double drop and we obtain surprising
ly good agreement between the continuum and lattice approaches. This is bec
ause long-wavelength concentration waves make the dominant contribution to
the divergent Huang scattering, with the remainder of the diffuse scatterin
g being very weak. We have also analysed the influence of elastic anisotrop
y on the diffuse scattering.