Abstract
The diffusion properties of an excess H atom adsorbed on a fully H-terminated Si(100)(2 × 1)-H surface have been analyzed by means of density functional theory-generalized gradient approximation calculations. Our diffusion pathway models consist of sequences of hops between metastable Si surface atomic structures with an excess H atom. We analyzed the reaction path and corresponding barrier height in each hop using the climbing image nudged elastic band method. The activation energies for diffusion along intra-dimer, intra-row, and inter-row pathways are found to be 0.11, 0.54, and 0.74 eV, respectively, which are quite small compared to the common H diffusion running with a vacant site of hydrogen termination. The weak adsorption energy of the excess H atom is responsible for the small activation energy of diffusion. The present diffusion mechanism suggests that the physical substance of the “hot atom mechanism” proposed in the previous investigations on H exposure onto the Si surface is related to the metastable structures of excessively adsorbed hydrogen atoms.
Highlights
It is essentially important to understand the diffusion process of H atoms on the Si surface for fundamental surface science[1,2,3,4,5,6,7,8,9] and for developing semiconductor device processes.[10–19] Some examples of the latter are the chemical vapor deposition (CVD) of Si thin films[10–14] and surface cleaning[15,16] or etching[17–20] of Si by H2 plasma at low temperatures
The activation energies for the paths along the intra-dimer, intra-row, and inter-row of Si(100) dimerized surfaces running with a vacant site of hydrogen termination have been reported as 1.46, 1.75, and 2.4 eV, respectively
We have explored the metastable structures of the Hterminated Si(100)(2 × 1) dimer surface with a single excess H atom
Summary
It is essentially important to understand the diffusion process of H atoms on the Si surface for fundamental surface science[1,2,3,4,5,6,7,8,9] and for developing semiconductor device processes.[10–19] Some examples of the latter are the chemical vapor deposition (CVD) of Si thin films[10–14] and surface cleaning[15,16] or etching[17–20] of Si by H2 plasma at low temperatures. The diffusion of H atoms on the clean or almost perfectly H-terminated Si(100) (2 × 1) surfaces has been intensively studied experimentally[1,2,3,4] and theoretically[4,5,6,7,9] as summarized in the recent review by Dürr and Höfer.[8] The activation energies for the paths along the intra-dimer, intra-row, and inter-row of Si(100) dimerized surfaces running with a vacant site of hydrogen termination have been reported as 1.46, 1.75, and 2.4 eV, respectively These high activation barriers are attributed to the strong covalent bond character as described in Ref. 8. Excess H atoms, can play important roles in CVD or etching processes in terms of high diffusivity
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