EMISSION CHANNELING

Hyperfine interaction techniques like Mossbauer effect or perturbed ga mma gamma angular correlation are commonly applied to study the struct ure and properties of impurity-defect complexes in solids. It is often difficult to resolve a certain defect structure unambiguously with th ese techniques, because an absolute determination of the lattice site of the probe atoms is not straight-forward. The emission channeling te chnique allows the direct determination of lattice sites of radioactiv e impurity atoms, incorporated into single crystalline solids. The cha nneling effects of electrons, positrons or alpha particles, emitted fr om radioactive impurities are measured along different crystal axes an d planes. From the measured anisotropic emission distributions the lat tice sites of the emitting atoms can be determined. Emission channelin g can be applied to a large variety of different probe atoms. Also, ra ther low impurity concentrations, comparable to those typically requir ed for hyperfine interaction techniques, are sufficient. In this contr ibution, the principles of the emission channeling technique, the expe rimental requirements and the quantitative analysis of emission channe ling spectra are reviewed. The capabilities and possibilities, which t he emission channeling technique offers, are highlighted by three rece nt experimental studies. First, studies of the diffusion of Ag in CdTe using transmutation doping with the electron emitting isotopes Ag-107 m and Ag-109m are described. Second, lattice location studies of As in diamond, which is a potential n-type dopant in this material, will be discussed. Third, an experiment is described to study the lattice loc ation of oversized impurities after low dose implantation into Fe. In this experiment, the unique decay properties of Fr-221 and Ra-221 are utilized to determine the lattice sites of five different impurity ato ms in a single alpha emission channeling measurement.