BORON-HYDROGEN COMPLEXES IN CRYSTALLINE SILICON

Boron-hydrogen complexes and the diffusion of hydrogen in boron-doped silicon are analyzed by means of Raman-scattering and infrared-reflection spectroscopies. At temperatures lower than 200-degrees-C, the hydrogen diffusion is controlled by a trapping at the acceptor sites, which becomes negligible at higher temperatures. Changes in the zone-center optical phonon of silicon and in the vibrational local modes of boron occur after hydrogen passivation. H and B local modes are studied as a function of temperature and external uniaxial stress. The analysis of the H-vibrational modes under stress reveals a nontrigonal symmetry of B-H complexes at 100 K, and a high mobility of hydrogen in these complexes. Our results are compared with different models proposed in the literature. We find that they are compatible with a "bond-minimum" site for hydrogen at low temperatures; however, under stress and at high temperatures, off-bond positions of H are proposed. We also analyze the stability of the boron-hydrogen complexes, and deduce a dissociation energy of 0.6 eV.