The quantitative determination of the static and dynamic properties of the locally stable states of monatomic H dissolved in crystalline Si: H+ , H0, and H- was described. The monatomic hydrogen atoms were created controllably near to room temperature by using the hole-stimulated dissociation of P-H (PH) complexes. Drift velocities and charge-change rates were studied via time-resolved capacitance-transient measurements in Schottky diodes under changes of bias. These data permitted the donor level of 2H to be located at about 0.16eV below the conduction band (confirming that the E3 center found in proton-implanted Si corresponded to interstitial H in undamaged Si), and the acceptor level at about 0.07eV below mid-gap, so that H was a negative-U system. The experimental values of donor level and acceptor level were consistent with predictions from first-principles calculations, which also provide detailed potential-energy surfaces for H in each charge state. While the phonon-mediated reaction H0 → H+ + e- was fast, the reaction H- → H0 + e- has an activation energy about 0.84eV, well above the energy difference (about 0.47eV) between initial and final states. The experiments also yielded diffusion coefficients near room temperature for 1H+, 2H+ and 2H–. The asymmetrical positioning of donor level and acceptor level in the gap accounts for many previously unexplained effects. For example, it was shown to be responsible for the much greater difficulty of passivating P-doped than comparably B-doped Si. And while modest hole concentrations dissociate PH complexes rapidly at temperatures where thermal dissociation takes years, no analogous dissociation of BH complexes by minority electrons, a process that was expected to be frustrated by the rapid thermal ionization of H0, could not be detected. The distribution of H in n-on-n epitaxial layers hydrogenated at 300C could be accounted for if the donor-H complexes were in thermal equilibrium with H2 complexes whose binding energy (relative to H2+ + H-) was of the order of 1.75eV. With this binding energy, the measured migration of H2 at 200C and below must be by diffusion without dissociation.

Energy Levels of Isolated Interstitial Hydrogen in Silicon. C.Herring, N.M.Johnson, C.G.Van de Walle: Physical Review B, 2001, 64[12], 125209 (27pp)