ANGULAR ANISOTROPY OF ELECTRON-EXCITED SECONDARY-ELECTRON EMISSION

We studied the influence of the crystalline structure of III-V compoun d semiconductors on the intensity of the energy distribution of second ary electrons. Modulation of the amplitude of the primary electron wav es within the crystal by electron-atom scattering results in a depende nce of secondary emission intensity on the incidence angle. We measure d the intensity anisotropy of the electron energy distribution in a wi de energy range on either GaAs(110) and InP(110) surfaces, for differe nt 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. Diffe rences in anisotropy of electrons with different probing depth is rela ted to the different relative importance of surface and bulk contribut ions to the overall emission intensity. Defocusing along forward scatt ering directions does not occur over a depth of several tens of angstr om, indicating that the defocusing length is longer than had been usua lly assumed for close-packed directions.