DONOR-HYDROGEN COMPLEXES IN CRYSTALLINE SILICON

Experimental results are presented on the study of Sb-H complexes in c rystalline silicon, employing Sb-119 --> Sn-119 source Mossbauer spect roscopy and a low-energy H implantation technique. In addition to a vi sible component, we observe a large decrease of the Mossbauer intensit y associated with the trapping of hydrogen, even at low temperatures. This is interpreted as the formation of a component with a negligible recoilless fraction. The different Mossbauer components were studied a s a function of H dose, II-implantation temperature and annealing temp erature. The data show that the visible component is associated with t he well-known SbH complex, whereas the invisible component is associat ed with the formation of SbHn (n greater than or equal to 2) complexes . We show that these complexes are in thermal equilibrium with a large r hydrogen reservoir (H-2), which governs their thermal stability. No Sb-H complexes are observed in p-type Si after II-implantation, in ag reement with the current belief that hydrogen has a deep donor level i n the gap. The microscopic structure of the various Sb-H and Sn-H comp lexes was studied with first-principles calculations using the pseudop otential-density-functional approach. The structure of the Sb-H comple x is found to be similar to the P-H complex, with the H in an antibond ing site of a Si atom neighbouring the Sb impurity. For SbH2 three con figurations are found with energies differing by less than approximate to 0.1 eV. We find that the reaction SbH + H reversible arrow SbH2 is exothermic. We argue that the SbH2 complexes are shallow donors, irre spective of the structure. Therefore, the formation of SbH2 may depass ivate the sample.