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The <100> split-interstitial

For the calculations of the electronic structure of the <100>split-interstitial in diamond, samples of 65 and 216 carbon atoms were used. The split-interstitial was created by replacing one carbon atom by two carbon atoms, displaced along the [100] and [$\bar{1}$00] directions from the lattice site. This initial configuration was then fully relaxed by slowly quenching the sample at a temperature of 300 K, by tight binding molecular dynamics.

Once the structure has been relaxed, the energy levels induced by the presence of the <100> split-interstitiala in the diamond lattice has been calculated by the tight binding model, using 60 special k-points. The results are shown in figure (10.4), together with the diamond DOS for direct comparison.

One can see that the presence of the split interstitial induces states exactly in the middle of the band gap, and occupied by two electrons. The dihedral angle between the two planes containing the three neighbors of each atom forming the interstitial pair has been calculated to be $\sim$ 89$^{\rm o}$. That is, to a good approximation, there is no mixing between the two orbitals centers on these atoms, which explains the mid-gap states. This founding is in good agreement with the results obtained from a more sophisticated methos mixing tight binding and density functional theory [19], although the authors did not mentioned the position of these states into the gap.

From the results shown above we can speculate that similarely to vacancies in diamond, the <100> split-interstitial interstitial is an n-type defect that could therefore contributes to compensatation in doped diamond. These two kinds of defects may be responsible for the difficulties accountered in doping diamond with phosphorus for example, since their presence are induced by the ion implantation process itself.


  
Figure 10.4: Density of electronic states (DOS) for the <100> split-interstitial in diamond (solid line), compared to the DOS of diamond (dashed line), calculated with 60 special k-points.
\begin{figure}\centerline{\epsfxsize=12.0cm \epsfbox{split65dos.eps}}
\end{figure}


next up previous contents
Next: Hydrogen in diamond Up: Electronic structure of defects Previous: Vacancy in diamond
David Saada
2000-06-22