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Direct observation of defect-mediated cluster nucleation

Nature Materials volume 1, pages 102–105 (2002)Cite this article

Abstract

Ion implantation is widely used to introduce electrically or optically active dopant atoms into semiconductor devices1. At high concentrations, the dopants can cluster and ultimately form deactivating precipitates2,3, but deliberate nanocrystal formation offers an approach to self-assembled device fabrication. However, there is very little understanding of the early stages of how these precipitates nucleate and grow1, in no small part because it requires imaging an inhomogenous distribution of defects and dopant atoms buried inside the host material. Here we demonstrate this, and address the long-standing question of whether the cluster nucleation is defect-mediated or spontaneous. Atomic-resolution illustrations are given for the chemically dissimilar cases of erbium and germanium implanted into silicon carbide. Whereas interstitial loops act as nucleation sites in both cases, the evolution of nanocrystals is strikingly different: Erbium is found to gather in lines, planes and finally three-dimensional precipitates, whereas germanium favours compact, three-dimensional structures.

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Figure 1: Determining the spatial resolution and sensitivity of the STEM.
Figure 2: HAADF images of the dislocations (marked by ┤, the horizontal dash symbolizes the additional SiC monolayer) at the edge of interstitial loops.
Figure 3: After annealing, HAADF imaging shows that the Er atoms have segregated in precipitates of widely differing sizes.
Figure 4: HAADF images showing the different arrangements of Ge atoms (introduced by ion implantation) at dislocation cores and their remnants after annealing for 180 s at 1,600 °C.

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Acknowledgements

We are grateful to Jim Choyke and Igor Khodos for discussions and Christian Schubert and Gunnar Pasold for ion implantation and annealing. This work has been supported by the German Foundation DFG SFB 196.

Author information

Authors and Affiliations

  1. Friedrich-Schiller Universität, Jena, 07743, Germany

    U. Kaiser

  2. Bell Laboratories, Lucent Technologies, Murray Hill, New Jersey, 07974, USA

    D.A. Muller & J.L. Grazul

  3. Boreskov Institute of Catalysis, Novosibirsk, 90, 630090, Russia

    A. Chuvilin

  4. JEOL USA, Peabody, 01960, Massachusetts, USA

    M. Kawasaki

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  1. U. Kaiser
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  2. D.A. Muller
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  3. J.L. Grazul
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  4. A. Chuvilin
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  5. M. Kawasaki
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Corresponding author

Correspondence to U. Kaiser.

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Supplementary information

FIGURE 1 A typical SiC matrix defect decorated by Er-atom columns together with the EELS spectrum of the Er M edge obtained from the single Er atom column the arrow is pointing to.

 FIGURE 2. An expanded view of the accordion or 'christmas-tree'-like Er cluster of Fig. 3c.This is a commonly observed Er structure. From the image contrast, each brighter dot contains approximately 10 or so Er atoms, so this is an end of view of a two-dimensional Errich platelet. (PDF 950 kb)

 FIGURE 3 HRTEM images of the dislocations at the edge of interstitial loops — (a) before and (b) after annealing for 180° sec at 1600 °C. Lattice bending maps showing the origins of the strains for (a) & (b) are shown in (c) & (d) respectively. (e) HAADF image of a dislocation before annealing.The white spots are isolated Er atoms scattered randomly about the matrix — none has yet segregated at the dislocation core. (f) After annealing the Er has segregated to the dislocations, and very little remains in the matrix. HRTEM from a JEOL 3010, HAADF from a JEOL 2010F. 

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Kaiser, U., Muller, D., Grazul, J. et al. Direct observation of defect-mediated cluster nucleation. Nature Mater 1, 102–105 (2002). https://doi.org/10.1038/nmat729

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