Angular anisotropy of electron-excited secondary electron emission

We studied the influence of the crystalline structure of III-V compound semiconductors on the intensity of the energy distribution of secondary electrons. Modulation of the amplitude of the primary electron waves within the crystal by electron-atom scattering results in a dependence of secondary emission intensity on the incidence angle. We measured the intensity anisotropy of the electron energy distribution in a wide energy range on either GaAs(110) and InP(110) surfaces, for different values of the primary beam energy between 0.6 and 5 keV. We focused our attention on the elastic and inelastic Auger emission and on the background intensity. The Monte Carlo method was used to simulate the sequences of events experienced by the primary and secondary electrons in the material. Anisotropy was assumed to arise in electron elastic focusing on atomic sites. The calculated anisotropy dependence on the electron kinetic energy is consistent with experimental results. Differences in anisotropy of electrons with different probing depth is related to the different relative importance of surface and bulk contributions to the overall emission intensity. Defocusing along forward scattering directions does not occur over a depth of several tens of angstrom, indicating that the defocusing length is longer than had been usually assumed for close-packed directions.