Radioactive probe atoms in semiconductors

Progress in semiconductor technology is accompanied by progress in knowledge and control of intrinsic and extrinsic defects in these materials, i.e. of vacancies or self-interstitials and dopant or impurity atoms, respectively. In spite of the large number of different experimental techniques, in particular electrical and optical ones, employed for the characterisation of these defects, there is a shortage of techniques that are able to identify the chemical nature, local structure, and dynamic properties of defects on an atomic scale. The missing sensitivity towards low defect concentrations in the range of 1016 cm-3 excludes many techniques which are known to fulfil these requirements. There is a growing number of experimental techniques, however, having in common the application of radioactive isotopes, so-called probe atoms, that deliver the required information also at low defect concentrations. Among the nuclear techniques, which will be discussed in context of their applicability to semiconductors, are the perturbed γγ angular correlation spectroscopy, Moessbauer spectroscopy, and β-nuclear magnetic resonance. But also non-nuclear techniques, such as the classical electrical and optical methods, being highly sensitive to low defect concentrations, will be shown to gain the missing sensitivity to the nature of defects if radioactive atoms are employed. For elemental semiconductors as well as for III-V, II-VI, and IV-IV compounds, it will be illustrated to what extent radioactive probe atoms contribute to delivering the needed knowledge and control of defects. (orig.)