In energetic (>500 eV) electron scattering along atomic chains the initial scattering events have a focusing effect, and subsequent events tend to be defocusing. We investigated the degree of forward focusing and the in-depth defocusing for 3-keV electrons along the Ga [110] regular chains in the zinc-blende structure. GaAs, GaP, and GaSb single crystals were used, to study the effect of the atomic environment in terms of both lattice parameters and partner atoms. Experimentally, the angular intensity distribution of elastic and inelastic (losses) Ga Auger electrons was monitored as a function of the incidence angle, to probe the in-depth anisotropy of primary electron-beam intensity. We found that forward focusing is enhanced up to a depth much larger than previously reported, and more than 30 scatterers are necessary to completely destroy the intensity anisotropy. Both focusing and defocusing along Ga chains are affected by the scattering potential of the partner, V-type atom, being larger in GaP than in GaAs and GaSb. Single scattering cluster (SSC) calculations including a broadening of 0.1 eV/Å in the primary beam energy satisfactorily describe the experimental findings. However, the progressive narrowing of the zeroth-order forward feature as the mean depth of origin of the electrons increases is not reproduced by SSC calculations and is possibly ascribable to multiple scattering.

• Received 31 July 1995

DOI:https://doi.org/10.1103/PhysRevB.52.14048