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Recently the detailed interpretation of positron-annihilation ␥-ray peak shapes has proven to be of interest with respect to their chemical specificity. In this contribution, we show highly resolved spectra for a number of different elements. To this purpose, annihilation spectra with strongly reduced background intensities were recorded in the two detector geometry, using a variable-energy positron beam. Division of the subsequently normalized spectra by a standard spectrum ͑in our case the spectrum of pure silicon͒ yields quotient spectra, which display features characteristic of the sample material. First we ascertain that the specific spectrum of an element is conserved in different chemical compounds, demonstrated here by identical oxygen spectra obtained from both SiO 2 /Si and MgO/Mg. Second, we show highly resolved spectra for a number of different elements ͑Fe . . . Zn, Ag, Ir . . . Au͒. We show that the characteristic features in these spectra vary in a systematic fashion with the atomic number of the element and can be tentatively identified with particular orbitals. Finally, for 26 different elements we compare the maximum intensity in the quotient spectra with the relative atomic density in the corresponding element. To our knowledge, this is the most comprehensive survey of such data made to date.

Electrical deactivation of arsenic in highly doped silicon has been studied using the positron-beam technique. Direct experimental evidence linking the formation of arsenic-vacancy complexes (i.e., Asn-v) to the deactivation process is reported. The average number of arsenic atoms per complex, n̄≳2, was determined by comparing the observed complex concentrations with those of the deactivated arsenic inferred from Hall-effect measurements.

Positron annihilation spectra of arsenic- and gold-implanted silicon are compared with spectra from bulk samples of arsenic and gold. Spectra with strongly reduced background intensities were recorded using a two detector coincidence system with a variable-energy positron beam. It is shown that features in the high-momentum region of the spectra (∼514–520 keV) can be identified with particular elements and that this identification is independent of structure, i.e., whether the element forms the bulk or is an implanted impurity. Proportionality between the intensity of characteristic spectral features and the fraction of annihilating positrons is also demonstrated, using the native oxide on a silicon wafer as a test case.