New models of clean and hydrogenated amorphous silicon surfaces

TL;DR

This paper introduces detailed atomistic models of amorphous silicon and hydrogenated amorphous silicon surfaces, revealing how surface structure influences electronic properties and passivation effects, advancing understanding of noncrystalline surface reconstruction.

Contribution

It provides new atomistic models of a-Si and a-Si:H surfaces using density functional theory, analyzing surface charge, electronic states, and vibrational modes to better understand surface reconstruction.

Findings

Surface structure correlates with surface charge density.

Hydrogen passivates dangling bonds and causes structural changes.

Resonant mixing occurs between bulk and surface defect states.

Abstract

We present new atomistic models of amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) surfaces. The a-Si model included 4096 atoms and was obtained using local orbital density functional theory. By analyzing a slab model (periodic in two dimensions with a slab about 44 \AA{} thick), we observed a strong correlation between surface structure and surface charge density, which might be compared to STM experiments. Hydrogen atoms added near the under-coordinated surface atoms passivate dangling bonds and induce structural rearrangements. We analyze the electronic structure, including the localization of the states, and note resonant mixing between bulk and surface defect structures. We also compute the classical normal modes of the hydrogenated a-Si and compare them to experiments where possible. Our work is a step toward understanding the meaning of ``surface reconstruction" for a noncrystalline material.