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

G. Kioseoglou Research Activities Research activities are focused on electrical spin injection and detection of spin polarized electrons into semiconductors. magnetic contacts ZnMnSe Fe FeGa MnGa tunnel barriers Shottky Al 2 O 3 MgO semiconductors GaAs QWs Si InGaAs Quantum Dots Essential Requirements for Spintronics Devices Efficient electrical injection Efficient spin transport Control of spin carriers Effective detection

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

G. Kioseoglou DMS as a spin contact :ZnMnSe n-ZnMnSe/AlGaAs/GaAs/AlGaAs spin-polarized electron injection giant Zeeman splitting ∆E=g  B H g e ~ 30; spin splittings >> kT 100% spin polarized optical polarization     GaAs ZnMnSe P circ = I (  +) - I (  -) I (  +) + I (  -) P spin = nn nn - + nn nn P spin = P circ (QWs) P spin = 2 P circ (bulk) PRB62, 8180 (2000)APL79, 3098 (2001)

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

G. Kioseoglou APL91, (2007) Spin injection from FeGa and MnGa into GaAs APL97, (2010) FeGa/Al 2 O 3 /GaAs MnGa/Al 2 O 3 /GaAs

G. Kioseoglou Silicon Spintronics Si / Si-Ge $ 120 Billion - extensive technology - extensive infrastructure 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 Long spin lifetimes for both donor-bound and free electrons in Si

G. Kioseoglou Electrical Spin Injection from Fe/Al 2 O 3 & Fe/SiO 2 into Si p-Si(001) substrate 150 nm p-Si 70 nm i-Si 70 nm n-Si Al 2 O 3 10 nm Fe ++ -- B.T. Jonker and G. Kioseoglou Nat. Phys. 3, 542 (2007) G. Kioseoglou et al, APL94, (2009) C.H. Li et al, APL95, (2009) P(TA) = 1.7 P(TO)

G. Kioseoglou Quantifying electron spin polarization from EL direct gap Optical polarization Electron spin polarization ^ T1T1 ^ L ^ T2T2  6 -  8 -  5  1  25'  so  7 +  8 +  15  2' indirect gap - the spin pol depends strongly on the phonon branch that mediates the opt transition Huge theoretical effort to understand spin orientation in Si p-type THEORY : P(TA) = 1.6 P(TO) Pengke Li and Hanan Dery, PRL105, (2010) 13% Experiment:P_TA sub =3.5% Spin injection efficiency 27%

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

G. Kioseoglou reduced growth rate reduced density increased uniformity in size

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

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

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

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

G. Kioseoglou

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

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