The time evolution of dopant passivation in p and n-type silicon Schottky and MIS barriers has been investigated for low-energy H ions implanted directly into the silicon through a 400-Å front-electrode metallization. Knowledge of the dependence of the near-surface hydrogen concentration on time and experimental parameters is crucial to the analysis of these experiments. Hydrogenation effects are observed to vanish at ion energies below 800 eV, which suggests that the front electrode, rather than being a source of H, will behave as a sink for H diffusing in the silicon. Accordingly, we show that a steady-state H concentration proportional to the ion-deposition flux and deposition depth is established in a time interval less than a second near the electrode. Although some of the mobile H appears to be in a positively charged state, we calculate that the bias voltage applied to samples has only a small influence on the near-surface H concentration. An extensive study of the effects of sample temperature, beam flux, and ion energy supports these concepts and has revealed no evidence of ion-damage induced H trapping. The possible importance of H.H recombination is suggested by data obtained at the higher H concentrations.