Atomic and electronic structures of a vacancy in amorphous silicon

Abstract

Locally, the atomic structure in well annealed amorphous silicon appears similar to that of crystalline silicon. We address here the question whether a point defect, specifically a vacancy, in amorphous silicon also resembles that in the crystal. From density functional theory calculations of a large number of nearly defect free configurations, relaxed after an atom has been removed, we conclude that there is little similarity. The analysis is based on formation energy, relaxation energy, bond lengths, bond angles, Voronoï volume, coordination, atomic charge and electronic gap states. All these quantities span a large and continuous range in amorphous silicon and while the removal of an atom leads to the formation of one to two bond defects and to a lowering of the local atomic density, the relaxation of the bonding network is highly effective, and the signature of the vacancy generally unlike that of a vacancy in the crystal.

On the Structure of Oxygen Deficient Amorphous Oxide Films

“…This view has recently been challenged in extensive calculations of amorphous Si. [ 48 ] Defect models can also be identified by analyzing structures responsible for localized states with energies in the band gap. [ 49 ] However, this identification is not unique either, as most defect structures are metastable and depend on the method of creation in both experimental and theoretical studies.…”

On point perforating defects in bilayer structures

“…Alas, this is often encountered and is described in detail in papers on amorphous silicon. 66,67 (2) There is a computational error caused by the insufficient size of created supercells. Due to the small size of supercells, which are computationally the cheapest to process using DFT, defects interact with their images, which leads to a nonphysical decrease in their formation energies.…”

In-situ Neutron Reflectometry to Determine Ge Self-Diffusivities and Activation Energy of Diffusion in Amorphous Ge0.8Si0.2

“…However, reports exist for the edge systems pure amorphous germanium [6,40] and silicon [39,27]. Recent computer calculations [54,55,57] suggest, that although the local order of amorphous silicon is close to that of crystalline silicon, the energetics of defect formation [54,55] and the diffusion mechanism [57] strongly differ. The formation energy of point defects such as vacancies, selfinterstitial and dangling bonds is negative [54,55].…”

“…Recent computer calculations [54,55,57] suggest, that although the local order of amorphous silicon is close to that of crystalline silicon, the energetics of defect formation [54,55] and the diffusion mechanism [57] strongly differ. The formation energy of point defects such as vacancies, selfinterstitial and dangling bonds is negative [54,55]. This means that defect production is spontaneous and does not need thermal energy in the case of the amorphous state which is contrary to the situation in the crystalline state.…”