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SEMICONDUCTOR SPINTRONICS

SEMICONDUCTOR SPINTRONICS. Spin as new degree of freedom in quantum device structures. George Kioseoglou Materials Science and Technology, University of Crete. Research Activities. tunnel barriers Shottky Al 2 O 3 MgO. magnetic contacts ZnMnSe Fe FeGa MnGa. semiconductors

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SEMICONDUCTOR SPINTRONICS

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  1. SEMICONDUCTOR SPINTRONICS Spin as new degree of freedom in quantum device structures George Kioseoglou Materials Science and Technology, University of Crete

  2. Research Activities • tunnel barriers • Shottky • Al2O3 • MgO • magnetic contacts • ZnMnSe • Fe • FeGa • MnGa • semiconductors • GaAs QWs • Si • InGaAs • Quantum Dots • Efficient electrical injection • Efficient spin transport • Control of spin carriers • Effective detection Essential Requirements for Spintronics Devices Research activities are focused on electrical spin injection and detection of spin polarized electrons into semiconductors.

  3. Growth and characterization MBE MBE • •MBE growth (NRL) • • Comprehensive characterization • • magnetic (SQUID, FMR) • • transport (Hall, etc) • • structural (TEM, x-ray diff) • • composition (XRF) • • magneto-optical • Theory and modeling

  4. DMS as a spin contact :ZnMnSe   Pcirc=     optical polarization n n - I(s+) - I(s-) n n I(s+) + I(s-) + ZnMnSe GaAs Pspin= n-ZnMnSe/AlGaAs/GaAs/AlGaAs • spin-polarized electron injection • giant Zeeman splitting ∆E=gBH • ge ~ 30; spin splittings >> kT • 100% spin polarized Pspin=Pcirc (QWs) Pspin = 2 Pcirc (bulk) PRB62, 8180 (2000) APL79, 3098 (2001)

  5. + - Fe metal semicond n-AlGaAs - i-GaAs    +  p-AlGaAs Fe AlGaAs Fe based GaAs Spin-LEDs APL80, 1240 (2002) APL82, 4092 (2003) APL84, 4334 (2004)

  6. Spin injection from FeGa and MnGa into GaAs FeGa/Al2O3/GaAs MnGa/Al2O3/GaAs APL91, 122515 (2007) APL97, 041103 (2010)

  7. Silicon Spintronics Si / Si-Ge $ 120 Billion Why Silicon Si is an ideal host for SpinS Low spin-orbit scattering is basic material property - low atomic mass - crystal inversion symmetry - low nuclear hyperfine interaction - extensive technology - extensive infrastructure Long spin lifetimes for both donor-bound and free electrons in Si

  8. Electrical Spin Injection from Fe/Al2O3&Fe/SiO2 into Si + - 10 nm Fe Al2O3 P(TA) = 1.7 P(TO) 70 nm n-Si 70 nm i-Si 150 nm p-Si p-Si(001) substrate B.T. Jonker and G. Kioseoglou Nat. Phys. 3, 542 (2007) G. Kioseoglou et al, APL94, 122106 (2009) C.H. Li et al, APL95, 172101 (2009)

  9. Quantifying electron spin polarization from EL p-type - G G 2' 8 G - G 15 6 D 1 G 25' + G D 8 D 5 + so G 7 THEORY : P(TA) = 1.6 P(TO) indirect gap - the spin pol depends strongly on the phonon branch that mediates the opt transition direct gap Optical polarization Electron spin polarization Huge theoretical effort to understand spin orientation in Si ^ ^ ^ L T2 T1 13% Experiment:P_TAsub=3.5% Spin injection efficiency 27% Pengke Li and Hanan Dery, PRL105, 037204 (2010)

  10. GaAs InAs 1 nm GaAs Fe based InAs QD Spin-LEDs • electrical spin injection up to RT • DP mechanism is suppressed

  11. reduced growth rate increased uniformity in size reduced density

  12. Filling of the electronic shell-states Continuous evolution of shell intensity with bias G. Kioseoglou et al, PRL 101, 227203 (2008)

  13. Another approach: P vs E Polarization exhibits maxima shifted with respect to intensity shell-peaks due to intershell exchange energy • first measurement of the s-p and p-d • intershell exchange energies • a significant step towards • understanding spin-polarized carriers in QDs Vxsp=13.5±1 meV Vxsp=7±2 meV G. Kioseoglou et al, PRL 101, 227203 (2008)

  14. IMPACT Fe/GaAs APL80, 1240 (2002) APL82, 4092 (2003) ZnMnSe/GaAs PRB62, 8180 (2000) Fe/Si Nat Physics3, 542 (2007)

  15. Collaborations Dr. Goswami (NRL)-microscopy Dr. Jonker (NRL) Prof. Petrou (SUNY Buffalo) Dr. Pawel Hawrylak Quantum Theory Group, Institute for Microstructural Sciences, Ottawa Prof. Hanan Dery University of Rochester, NY THEORY

  16. Theory: 2 e-h pairs/QD – Sz=-1 s-shell exciton s-shell hole + p-shell elec s-p exchange between spin polarized electrons σ + The outgoing photon carries the initial-state exchange energy of the spin-polarized electrons Initial state Final state

  17. + Fe - n-AlGaAs - i-GaAs + p-AlGaAs 100 mm

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