Dislocations as Sinks for Self-Interstitials in Gold Doped Float Zone Silicon
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DISLOCATIONS AS SINKS FOR SELF-INTERSTITIALS IN GOLD DOPED FLOAT ZONE SILICON
G. MAR IANI*, B. PICHAUD*, W. J. TAYLOR-- AND W.-S. YANG-*Laboratoire de Physique Cristalline,U.A. 797 C.N.R.S., Univ. Aix-Marseille III, 13397 Marseille Cedex 13, France **Dept.of Mechanical Engineering and Materials Science, Univ.,
Duke
Durham NC 27706
ABSTRACT Self-interstitial sink efficiencies of dislocations y were measured in gold doped FZ (111) and (100) samples, we found respectively y-0.4-0.5 and y=0.2-0.3. y is probably sensitive to dislocation character and to the deformation process.
INTRODUCTION Gold doping reduces minority-carrier diffusion lengths and thus improves fast recovery device switching. However, leak currents due to gold segregation along dislocations are often obtained [1]. On the other hand, the control of the reverse recovery time trr of a device can be disturbed by gettering effects due to dislocations which modify the substitutional gold atom distribution. Therefore, it is essential to understand golddislocations interactions in order to anticipate the dislocationinduced decay of device performances. In silicon gold diffuses very quickly using interstitial site Aui (Di = 7.2 10- 6 cm2 s-1 at 1000'C [2)) then it transforms into electrically active substitutional site Au. via the kick-out mechanism [3] Aui --- > Au. +Sii Self-interstitials (Sii) can be annihilated through sinks: the surface in dislocation free silicon (4] and dislocations in deformed silicon [5]. Therefore, an enrichment in substitutional atoms Aus in the vicinity of dislocations may be expected. 4 Provided that the dislocation density ND ranges between 10 cm-2 7 2 and 10 cm- , the substitutional gold concentration NAus is controlled by the average distance between dislocations [7]. 1/2
NAuS = N u3As2 (Dt 1
with
1=
2D 'y ND
Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
(1)
82
lim NAus is
the
solubility
limit
of
substitutional
gold
at
the
diffusion temperature,DI the effective diffusivity of Sii ,t the annealing time and y is a geometrical efficiency factor which theoretically should be not far from 1. In highly dislocated Silicon (ND>10 7 cm- 2 ) the sink density is high enough to eliminate all the Sii produced. Sink efficiencies were already evaluated by several authors: Stolwijk et al. [6] reported a value near 1, Yang et al. (7] found 0.1
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