Hybrid superconductor–semiconductor devices made from self-assembled SiGe nanocrystals on silicon


The epitaxial growth of germanium on silicon leads to the self-assembly of SiGe nanocrystals by a process that allows the size, composition and position of the nanocrystals to be controlled. This level of control, combined with an inherent compatibility with silicon technology, could prove useful in nanoelectronic applications. Here, we report the confinement of holes in quantum-dot devices made by directly contacting individual SiGe nanocrystals with aluminium electrodes, and the production of hybrid superconductor–semiconductor devices, such as resonant supercurrent transistors, when the quantum dot is strongly coupled to the electrodes. Charge transport measurements on weakly coupled quantum dots reveal discrete energy spectra, with the confined hole states displaying anisotropic gyromagnetic factors and strong spin–orbit coupling with pronounced dependences on gate voltage and magnetic field.

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Figure 1: Structure and growth of SiGe self-assembled nanocrystals and device layout.
Figure 2: SiGe single-hole supercurrent transistor.
Figure 3: Tunnelling spectroscopy measurements on a high-resistance device.
Figure 4: Anisotropy and gate dependence of the hole g-factors.
Figure 5: Anisotropic spin–orbit coupling strength probed by inelastic co-tunnelling.


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The authors thank T. Haccart and the PTA cleanroom team of CEA, J.-L. Thomassin and F. Gustavo for their help in device fabrication, and T. Fournier for helpful discussions and providing free access to fabrication recipes and equipment at the NANOFAB facility of the Néel Institute. We also acknowledge helpful discussions with M. Houzet, V. Golovach, W. Wernsdorfer, D. Feinberg, G. Usaj, R. Whitney, M. Sanquer, X. Jehl, G. A. Steele and E. J. H. Lee, and support from the Agence Nationale de la Recherche (through the ACCESS and COHESION projects). G.K. acknowledges further support from the Deutsche Forschungsgemeinschaft (grant no. KA 2922/1-1).

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G.K. and S.D.F. planned the experiment, interpreted the data and co-wrote the paper. G.K. fabricated the devices, performed the measurements with P.S. and S.D.F., and analysed the data. P.S. participated in the data analysis and set up the dilution refrigerator. M.S. grew the SiGe self-assembled nanocrystal samples. F.F. fabricated the non-standard SOI wafers. M.M., V.B. and F.L. provided important help in device fabrication. A.R. and O.G.S. supervised the growth of the self-assembled SiGe nanocrystals. All authors discussed the results and commented on the manuscript.

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Correspondence to G. Katsaros or S. De Franceschi.

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Katsaros, G., Spathis, P., Stoffel, M. et al. Hybrid superconductor–semiconductor devices made from self-assembled SiGe nanocrystals on silicon. Nature Nanotech 5, 458–464 (2010). https://doi.org/10.1038/nnano.2010.84

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