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Single-crystal germanium layers grown on silicon by nanowire seeding

Abstract

Three-dimensional integration and the combination of different material systems are central themes of electronics research. Recently, as-grown vertical one-dimensional structures have been integrated into high-density three-dimensional circuits. However, little attention has been paid to the unique structural properties of germanium nanowires obtained by epitaxial and heteroepitaxial growth on Ge(111) and Si(111) substrates1,2, despite the fact that the integration of germanium on silicon is attractive for device applications. Here, we demonstrate the lateral growth of single crystal germanium islands tens of micrometres in diameter by seeding from germanium nanowires grown on a silicon substrate. Vertically aligned high-aspect-ratio nanowires can transfer the orientation and perfection of the substrate crystal to overlying layers a micrometre or more above the substrate surface. This technique can be repeated to build multiple active device layers, a key requirement for the fabrication of densely interconnected three-dimensional integrated circuits.

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Figure 1: SEM micrographs of the samples at various points in the processing sequence.
Figure 2: TEM micrographs of crystallized germanium islands.
Figure 3: EBSD analysis of a 30 µm × 30 µm germanium island after LPE.
Figure 4: In-plane electrical measurements of crystallized germanium islands (100 nm thick), with crystallization processes as described in Fig. 2a and b, respectively.
Figure 5: Estimated growth velocity scaled by homogeneous and heterogeneous nucleation rate versus temperature for a 30 µm × 30 µm germanium island with thin-film thicknesses of 30 nm, 100 nm and 1 µm encapsulated in SiO2.

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Acknowledgements

The authors thank the members of the Nanowire Facility at Stanford University, I. A. Goldthorpe, J. Ratchford, J. Woodruff, Y. Zhang and H. Adhikari for helping maintain the nanowire growth reactor, and J. McVittie and Y. Nishi for managing the facility. The authors also thank T. Brand and R. Macdonald for help in the CMP process and J. Feng for useful discussions. Funding for this work was provided by the DARPA SPAWAR 3D-IC programme, a Stanford School of Engineering Fellowship and a Stanford Graduate Fellowship.

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All authors discussed the results and commented on the manuscript. S.H. and P.C.M. conceived and designed the experiments, analysed the data and co-wrote the paper. S.H. and P.W.L. performed the experiments. A.F.M. contributed TEM sample preparation and analysis.

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Correspondence to Paul C. McIntyre.

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Hu, S., Leu, P., Marshall, A. et al. Single-crystal germanium layers grown on silicon by nanowire seeding. Nature Nanotech 4, 649–653 (2009). https://doi.org/10.1038/nnano.2009.233

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