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Past Work:  Impurity Effects 

Transition-metal impurities degrade the minority charge-carrier lifetime in silicon.  But the severity of the degradation can vary considerably from one impurity to another, and also is modified in some cases by pairing with other impurities, such as the commonly used dopants.  We have grown a number of controlled samples with various Fe impurity concentrations. The table below shows that the severity of lifetime degradation is greater when both Fe and Ga are present than when either one exists alone in the Si crystal. The figure shows deep-level transient spectroscopy on one of these samples (done in collaboration with Georgia Institute of Technology), from which we are able to obtain information about capture cross sections and trap levels.

Additional impurity studies have included hydrogen, nitrogen, oxygen, and carbon as well as the dopants boron, gallium, indium, and aluminum.  A new solid-source doping method for B in FZ grown silicon crystals is reported at the 15th American Conf. on Crystal Growth and Epitaxy (ACCGE-15), July 20-24, 2003 and will be published in J. Crystal Growth. 

Crystal

Resistivity

(W-cm)

Ga

(cm-3)

Fe Target

(cm-3)

Lifetime (µs)

41121 a

3.5

3.8 x 1015

0

> 1400

51129-1

24,000

0

1.2 x 1014

12

70515

6

2.2 x 1015

4.8 x 1011

2.2

51212-1a

4.1

3.3 x 1015

1.3 x 1014

0.40

51212-1b

1.4

1 x 1016

1.3 x 1014

0.34

dltsfega.gif (16037 bytes)
_________________
T.F. Ciszek, T.H. Wang, W.A. Doolittle, and A. Rohatgi, “Minority-Carrier Lifetime Degradation in Silicon Co-Doped with Iron and Gallium,” in: 26th IEEE Photovoltaic Specialist Conf. Record, Anaheim, CA, Sept. 29-Oct. 3, 1997 (IEEE, New Jersey, 1997) pp. 59-62.

Siliconsultant, P.O. Box 1453, Evergreen, CO 80437 USA                 §§§§§                  e-mailted_ciszek@siliconsultant.com

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