Self-assembled SiGe single hole transistors

Transcription

1 Self-assembled SiGe single hole transistors G. Katsaros 1, P. Spathis 1, M. Stoffel 2, F. Fournel 3, M. Mongillo 1, V. Bouchiat 4, F. Lefloch 1, A. Rastelli 2, O. G. Schmidt 2 and S. De Franceschi 1 1 CEA Grenoble, LaTEQS Laboratory,France 2 IFW-Dresden, Germany 3 CEA Grenoble, LETI, France 4 CNRS-Grenoble, Neél Institute, France Georgios Katsaros Aussois 2010

2 The Stranski-Krastanow growth mode Si (001) Ge Ge Lattice-mismatched SK-growth. E.g. Ge/Si(001) Wetting layer (WL) formation Spontaneous formation of 3D islands Competition: elastic energy relaxation vs surface energy

3 The Ge/Si(001) System 50x32x7 nm 3 50x50x7 nm 3 50x50x10 nm 3 110x110x27 nm 3

4 Why are SiGe self-assembled quantum dots interesting? Nominally pure Ge islands contain Si Ge content bigger close to the apex of the islands Si content increases the higher the growth temperature Strain relaxation towards the apex of the islands T. U. Schülli et al. Phys. Rev. Lett. 90, (2003) G.K. et al., Phys. Rev. B 72, (2005) PhD Thesis, Konstanz 2006

5 Controlling the position of SK quantum dots SK quantum dots localize on nanoscale grooves G. K. et al., Phys. Rev. Lett. 101, (2008) PhD Thesis Konstanz 2006

6 Controlling the position of SK quantum dots Growth on patterned substrates O.G. Schmidt Group, IFW Dresden

7 Hole quantum confinement in a SiGe quantum-dot transistor QUALITATIVE BAND DIAGRAM Metal source contact Si tunnel barrier Ge quantum dot Si tunnel barrier Metal drain contact

8 State of the art for p-type SiGe nanostructures Lu et al., PNAS 102, (2005) Hu et al., Nat. Nanotechn. 2, 622 (2007) Xiang et al., Nat. Nanotechn. 1, 208 (2006)

9 State of the art for p-type SiGe nanostructures Roddaro et al., PRL (2008) Small dots g ~ 2

10 Single-hole transport in weakly coupled devices C)

11 Single-hole transport in weakly coupled devices Coulomb blockade conductance peaks C)

12 Low-temperature single-hole transport Excitation lines (Energy-level spacing of a few mev due to size confinement in the SiGe island)

13 Zeeman splitting of quantum-dot hole states Direct tunneling spectroscopy G.K. et al., Nature Nanotechnology 5, 458 (2010)

14 Zeeman: Hz ~ -2kμ B B J Band Structure of SiGe g=6k g=2k g~0 g=4k Haendel et al., PRL 96, (2006) Composition dependent Luttinger parameter k: Ge: Si: % Ge: %Ge Fraj et al., Semiconductor Science and Technology 23, (2008). Fraj et al., J. Appl. Phys. 102, (2007).

15 Zeeman: Hz ~ -2kμ B B J Band Structure of SiGe g=6k g=2k g~0 g=4k Haendel et al., PRL 96, (2006) Composition dependent Luttinger parameter k: Ge: Si: % Ge: %Ge Fraj et al., Semiconductor Science and Technology 23, (2008). Fraj et al., J. Appl. Phys. 102, (2007). Nenashev et al., Phys. Rev. B 67, (2003)

16 Sequential Spin filling V sd 8 T 7 T 6 T 5 T N+1 N N-1 V g

17 Sequential Spin filling V sd 8 T 7 T 6 T 5 T N+1 N N-1 V g 8 T 7 T 6 T 5 T

18 Inelastic cotunneling (strong coupling) Can be used for spectroscopy [De Franceschi et al, PRL 86, 878 (2001)] Resolution determined by temperature and not by life-time broadening! Flat featurelless differential conductance within coulomb diamond

19 Inelastic cotunneling (strong coupling) Can be used for spectroscopy [De Franceschi et al, PRL 86, 878 (2001)] Resolution determined by temperature and not by life-time broadening! ev = δ δ V sd N+1 N N-1 V g Step in differential conductance

20 Zeeman splitting measured by spin flip inelastic cotunneling

21 Zeeman splitting measured by spin flip inelastic cotunneling

22 Summary of g-factor results

23 Measuring the spin-orbit coupling strength

24 Measuring the spin-orbit coupling strength

25 Measuring the spin-orbit coupling strength

26 Measuring the spin-orbit coupling strength N. Roch et al., Nature 453, 633 (2008)

27 Measuring the spin-orbit coupling strength

28 Measuring the spin-orbit coupling strength

29 Measuring the spin-orbit coupling strength G. K. et al., Nature Nanotechnology 5, 458 (2010)

30 Measuring the spin-orbit coupling strength G. K. et al., Nature Nanotechnology 5, 458 (2010)

31 Summary First realization of three terminal devices based on SiGe self-assembled nanocrystals Low temperature measurements indicate strongly anisotropic hole g-factors Tunable spin-orbit coupling strength is demonstrated Outlook