D-Defects Detected by ELYMAT Technique

With the ELYMAT (a special technique to map minority carrier lifetime in Si; see the publications in the link), D-defects and other microdefects in Si can be "seen" in some cases because they decrease the minority carrier life time (they act as recombination centers).
The pictures obtained monitor the local photo current (induced by a scanned Laser beam) in special electrolytic junctions. It is a direct measure of the minority carrier life time. A typical picture of state-of-the-art as-grown 150 mm Si wafers from around 1990 is shown below. Bright areas correspond to decreased life times.
The most outstanding feature is the well-defined ring. It is due to small defects incorporating SiO2.
With hindsight gained by much research in the nineties, the situation is as follows: Inside the oxygen-precipitate ring, small vacancy agglomerates (in the form of octahedral little voids) dominate; outside the ring, interstitials agglomerates (probably in the form of small stacking faults and dislocation loops (the old "classical" swirl defects)) were formed.
This rather unique defect pattern is the result of the complicates interaction of three main point defects: vacancies, Si-interstitials and O-interstitials. Whereas the above interpretation is now universally accepted, the details about the primary defects are not yet known beyond reasonable doubt.
For a recent review read the paper of Bob Falster and V.V. Voronkov.

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go to 1.3.3 The larger View and Complications

© H. Föll (Defects - Script)