Donor level of bond-center hydrogen in germanium

We apply Laplace deep-level transient spectroscopy (LDLTS) in situ after low-temperature proton implantation into crystalline n-type germanium and identify a deep metastable donor center. The activation energy of the donor emission is similar to110 meV when extrapolated to zero electric field. We obtain the split patterns of the emission signal for uniaxial stress applied along three major crystal directions <100>, <110>, and <111>, and conclude that the symmetry of the center is trigonal. We compare the annealing characteristics with those of bond-center hydrogen in silicon and with those of a trigonal center in germanium previously identified as bond-center hydrogen by in situ local-mode infrared absorption spectroscopy. From this comparison it is concluded that the observed donor emission originates from bond-center hydrogen. Infrared absorption also revealed another trigonal center tentatively ascribed to hydrogen occupying an antibonding configuration. A search for a corresponding deep level (as a hole or electron trap) failed, indicating that such level must be near midgap or resonant with (close to) the valence band.