A New Method to Determine the Chemical Composition and Structure of Non-Elemental Acceptor and Donor Centers in Ultra-Pure Germanium

A new approach towards the understanding of hitherto unknown, non-elemental acceptors and donors which can limit the purity of ultra-pure germanium has been explored for a specific pair of shallow centers, designated A2 and D. Using photoelectric spectroscopy, we have demonstrated that an isotope shift in the ground-state binding energy occurs when the germanium crystals are grown in pure deuterium instead of in the usual pure hydrogen atmosphere. This isotope shift is the most direct proof of the presence of hydrogen atoms in the centers A2 and D. Applying uniaxial stress to Ge samples containing A2 and D, we show that the symmetry and structure of the centers can be explored. The knowledge of the chemical composition and the structure of the nonelemental centers will allow development of methods to reduce and keep their concentrations to acceptable levels.