2008, Vol.11, No.3, pp.316-326

To explain the effect of electron density saturation at high phosphorus concentrations the model of negatively charged phosphorus clusters was compared with experimental data. A number of negatively charged clusters incorporating a point defect and phosphorus atoms (DP₁)^-, (DP₂)^-, (DP₂)^2-, (DP₃)^-, (DP₃)^2-, (DP₄)^-, and (DP₄)^2- were investigated at temperatures of 920 and 1000 ^oC. It was established that for clusters incorporating more than one phosphorus atom the calculated electron density reached a maximum value and then decreased monotonically and slowly with an increase in the total dopant concentration. If a cluster incorporates 3-4 phosphorus atoms, the calculated dependencies of carrier concentration agree well with the experimental data for both temperatures regardless of the negative charge state of the cluster (- or 2-). Moreover, for all doubly negatively charged clusters investigated the fitting parameter is independent of the temperature. It is very convenient in view of the clustering phenomena simulation. From the good agreement of the calculated curves with the experiments it follows that the model based on the formation of negatively charged clusters can be used in simulation of high concentration phosphorus diffusion.
Key words: clusters, diffusion, doping effects, phosphorus, silicon

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