Chemical Origin of the Grain Boundary Carrier Recombination in Silicon Bicrystals
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CHEMICAL ORIGIN OF THE GRAIN BOUNDARY CARRIER RECOMBINATION IN SILICON BICRYSTALS
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F. BATTISTELLA', A. ROCHER" and A. GEORGE" Laboratoire d'Optique Electronique du C.N.R.S. 29 rue Jeanne Marvig, 31400 TOULOUSE (FRANCE) Laboratoire de Physique du Solide de l'E.N.S.M.I.M. Parc de Saurupt, 54042 NANCY CEDEX (FRANCE)
ABSTRACT The minority carrier recombination related to grain boundaries is studied by the SEM/EBIC technique. The specimens investigated are silicon bicrystals obtained by the Czochralski pulling process. The specimens are heated for 2 hours at 750"C in a neutral atmosphere. Heterogeneous recombination of the grain boundaries is then observed. X-Ray topography and Transmission Electron Microscopy (TEM) have been performed to determine the origin of the heterogeneous recombination. A direct relationship between the local recombination along the grain boundary and the precipitates localized at the interface has been established. The chemical origin of the precipitates is discussed. INTRODUCTION The origin of minority carrier recombination associated with the grain boundary in silicon is often related to the existence of dangling bonds in the core of the defect. This idea has been developed in the same way as those proposed for amorphous silicon. Grain boundary passivation by atomic hydrogen was first interpreted as saturation of dangling bonds /I/. Nevertheless, a passivation effect with molecular hydrogen has been also observed. In addition it has been shown that the grain boundary electrical activity is usually increased by heat treatment /2/. Such results cannot be directly related to dangling bond effects. The purpose of this paper is to show that the origin of grain boundary electrical activity is mainly related to an impurity effect. Three different techniques of characterization have been used to establish this result : The SEM/EBIC technique images directly the recombination sites that are responsible for the electrical activity. X-ray topography shows the difference interface before and after the heat treatment. Transmission Electron Microscopy (TEM) defects in the interface.
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Mat. Res. Soc. Symp. Proc. Vol. 59. -1986 Materials Research Society
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SAMPLE PREPARATION The specimens investigated are obtained from silicon bicrystals, which are grown by a special Czochralsky pulling process, developed by Aubert et al. /3/. Two bicrystal configurations have been studied (221)/(221) z9 and (710)/(710)2:25. Silicon is N-type with a resistivity of 10flcm. The sizes of the samples were 10x10xO.5 mm3. The specimens are thermally treated to modify the impurity distribution. The heat treatment is performed at 750"C for 2 hours in a nitrogen or argon atmosphere. The samples are pulled out of the hot zone over a period of a few seconds and put under an intense nitrogen jet to avoid rapid cooling. In order to perform EBIC observations, a charge collection system is provided by a Schottky diode. Circular diodes consist of a 30 nm layer of chromium deposited by evaporatio
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