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Abstract
Silicon germanium alloys are technologically important in microelectronics but also they are an important paradigm and model system to study the intricacies of the defect processes on random alloys. The key in semiconductors is that dopants and defects can tune their electronic properties and although their impact is well established in elemental semiconductors such as silicon they are not well characterized in random semiconductor alloys such as silicon germanium. In particular the impact of electronegativity of the local environment on the electronic properties of the dopant atom needs to be clarified. Here we employ density functional theory in conjunction with special quasirandom structures model to show that the Bader charge of the dopant atoms is strongly dependent upon the nearest neighbor environment. This in turn implies that the dopants will behave differently is silicon-rich and germanium-rich regions of the silicon germanium alloy.
Highlights
The reasoning and efficacy of special quasirandom structures (SQS) to describe Si1-xGex alloys and other related random alloys has been discussed extensively in previous work and here we will only briefly discuss this approach for completeness[24,25]
For disordered random alloys the analogous approach is not practically feasible as it requires the construction of very large supercells (>103 atoms)[17] with the atoms being randomly positioned at the lattice sites
The advantage of the SQS method is that it efficiently mimics the statistics of random alloys with small supercells[25] and this allows the practical application of density functional theory (DFT) in materials were many defect calculations are needed[18,19,20,21,22,23]
Summary
We employ density functional theory in conjunction with special quasirandom structures model to show that the Bader charge of the dopant atoms is strongly dependent upon the nearest neighbor environment. Relaxation and thermodynamics impact the defect processes and the electronic properties of the defects (for example charge transfer) can influence the properties of Si1-xGex and in that respect the local environment is anticipated to play www.nature.com/scientificreports
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