ESD of nonthermal halogen atoms from In-doped (001) KBr

We have measured the kinetic energy distributions of neutral halogen atoms emitted due to electron-stimulated desorption (ESD) from In-doped (001)KBr single crystals. The concentration of In⁺ in investigated samples varied between 10¹⁷ and 10²⁰ particles/cm³. The measurements were performed at target temperature of 150°C. In all cases the energy spectra consist of two peaks. The distribution of low-energy particles can be described by the thermal (Maxwellian) energy spectrum. Particles contributing to the second peak have nonthermal kinetic energies. The emission of halogen atoms having nonthermal energies decreases with an increase in the concentration of In impurities. At the same time, the emission of thermal particles does not seem to be sensitive to variation of In⁺ concentration. At the temperatures of interest here, In⁺ impurities are known to be very efficient traps for migrating holes but not to influence the migration of H-centers. The obtained results support the model of nonthermal halogen desorption which requires a long range diffusion of holes from the bulk to the surface as a necessary step of the process.