Iron concentration determination

The exact determination of the iron concentration is very important, since iron is one of the most abundant and also most detrimental defects in silicon. (Alttext kürzen, da zu lang))

With the MDPingot and MDPmap series it is possible to measure the iron concentration in bricks and wafers fully automated and with a very high resolution.

Lifetime measurements before and after iron boron pair dissociation is a widely used method for iron determination in silicon wafers.

In boron doped silicon with a high doping concentration, as it is used for PV applications nearly 100 % of the electrical active iron is present as FeB pairs. With light of sufficient energy these pairs can be dissociated in Fe_i and B. This process is reversible and after some time all FeB pairs are associated again. FeB and Fe_i have different recombination properties, so that the dissociation has an effect on the measured lifetime. With this effect the iron concentration can be determined via:

$[\mathrm{Fe}] = C(\Delta n) \cdot \left( \cfrac{1}{\tau_{\mathrm{Fe}_i}} - \cfrac{1}{\tau_{\mathrm{FeB}}} \right)$

For the iron determination a calibration factor C is used, which depends on the injection, doping concentration and trap concentration, which has to be considered especially in Multicrystalline silicon. With MDP a determination of the iron concentration is possible for mc- and mono-Si with a high resolution and thanks to simulations and years of research, also with a high accuracy.