Donor-hydrogen complexes in crystalline silicon

Experimental results are presented on the study of Sb-H complexes in crystalline silicon, employing Sb-119 --> Sn-119 source Mossbauer spectroscopy and a low-energy H implantation technique. In addition to a visible component, we observe a large decrease of the Mossbauer intensity 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 as a function of H dose, II-implantation temperature and annealing temperature. The data show that the visible component is associated with the well-known SbH complex, whereas the invisible component is associated with the formation of SbHn (n greater than or equal to 2) complexes. We show that these complexes are in thermal equilibrium with a larger hydrogen reservoir (H-2*), which governs their thermal stability. No Sb-H complexes are observed in p-type Si after II-implantation, in agreement with the current belief that hydrogen has a deep donor level in the gap. The microscopic structure of the various Sb-H and Sn-H complexes was studied with first-principles calculations using the pseudopotential-density-functional approach. The structure of the Sb-H complex is found to be similar to the P-H complex, with the H in an antibonding site of a Si atom neighbouring the Sb impurity. For SbH2 three configurations 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, irrespective of the structure. Therefore, the formation of SbH2 may depassivate the sample