Introduction

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 could be dissociated in Fei and B. This process is reversible and after some time all FeB are associated again. FeB and Fei have different recombination properties, so that the dissociation has a effect on the measured lifetime. With this effect the iron concentration can be determined via:

Aim

The aim is to measure the iron concentration as exactly and fast as possible, with a very high resolution.

Solution

With the novel developed tools MDPingot and MDPmap09 it is possible to measure the iron concentration very exactly. A calibration factor C is used, which is dependent of the injection, doping concentration and trap concentration, which has to be considered especially in multicrystalline silicon. With MDP (microwave detected photoconductivity) 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.

Result

The MDPingot allows to monitor the iron content in ingots, so an investigation of the reasons of the impurity is possible that at a very early process step. Furthermore an investigation of the influence of iron on the efficiency of the solar cells is possible. dresolution, so that the exact location of the electrically active iron can be located, for example if it is predominantly located at grain boundaries.

For more information about the iron determination and the dependencies of the calibration factor read:

[1] S. Rein and S. W. Glunz, Journal of Applied Physics 98 (2005).

[2] N.Schüler, T.Hahn, K. Dornich, J.R. Niklas, Solid State phenomena to be published