Spectroscopic studies of point defects in silicon and germanium

Abstract

The electronic structure of point defects in silicon and germanium is discussed. After some general remarks on defects generated by doping with elements from group III and V in the Periodic Table, special attention is given to defects with binding energies of the ground state much larger than those predicted by the effective mass theory (EMT) such as double donors (group VI) and double acceptors (group II) as well as transition metals. All these point defects exhibit sharp line spectra in absorption and photoconductivity which allow detailed studies of their electronic structure including states which are not seen in optical dipole transitions. As an example, detailed results are given on spin triplet states and avoided crossings of double donors in silicon. It is shown that the excited Coulomb states of these point defects are well described by the EMT.