Reactions of excess hydrogen at a Si(111) surface with H termination: First-principles calculations

Hydrogen reactions with silicon substrates is an established technique for the study and control of surface morphology. Here, we report the results of first-principles calculations on the trapping and depassivation reactions involving excess hydrogen (x-H) at a fully H-passivated Si(111) surface. We find that x-H atoms can depassivate Si-H bonds with a small barrier of 0.8 eV, or they can get trapped in very stable configurations that comprise of a dihydride and a vicinal Si-H bond. Desorption of H-2 molecules from these complexes has an activation energy of 1.68 eV, which can account for pertinent experimental data. We discuss also the effect of strain on the possibility of altering the x-H surface profile.