Saroj P. Dash. Chalmers University of Technology. Göteborg, Sweden. Microtechnology and Nanoscience-MC2

Transcription

1 Silicon Spintronics Saroj P. Dash Chalmers University of Technology Microtechnology and Nanoscience-MC2 Göteborg, Sweden

2 Acknowledgement Nth Netherlands University of Technology Sweden Mr. A. Dankert Dr. R. Jansen Dr. M. de Jong Mr. S. Sharma Ma Planck Institute Stuttgart, Germany Prof. H. D. Carstanjen

3 Outline Introduction to spin injection into silicon Spin injection into silicon at room temperature Inverted Hanle effect Control of spin polarization in Silicon 2DEG

4 Present and future of electronics Silicon MOSFET scaling for smaller and faster transistor nm 32 nm 22 nm Materials limitations Device leakage Power consumption Opportunities for new technology: Spin-Electronics 1 0

5 Opportunities for new technology Silicon spintronics Semiconductor chip Magnetic hard disc Process information Storage information Can we develop spin based transistors, switches and logic circuits based on silicon?

6 Electrical creation of spin polarization in silicon Ferromagnet Arnov Proposal Semiconductor μ Arnov, Sov. Phys. Semicond. 10, 698 (1976) Non-equilibrium spin polarization

7 Silicon spintronics Injector Detector Ferromagnet Tunnel Barrier Silicon Longer spin life time in Si Low spin orbit coupling Low hyperfine interaction Spin Injection Transport Detection Manipulation Room Temperature n- and p- type Si

8 Hot electron spin injection into silicon Spin valve signal 70 K In plane magnetic field (Oe) Applebaum et al. Nature 447, 295 (2007)

9 Tunnel spin injection - Optical detection Spin injection via tunneling - Si n-i-p LED - top layer 80 nm n-type Si ( cm -3 ) Circular lig ght polariza ation (%) T = 50 K Spin-polarized electrons Recombination with holes Circularly polarized emission Magnetic field (T) Jonker et al. Nature phys. 3, 542 (2007)

10 Electrical detection of spin injection in GaAs Non-local measurement geometry I V e s FM s FM L >> L SD L < L SD GaAs Spin valve signal 50 K GaAs X. Lou et al., Nature Physics 3, 197 (2007)

11 Electrical detection of spin injection in Si I Injector Detector V e s FM TB s FM TB L>>L L SD L<L L SD 2 μm Silicon Spin valve signal at 5 K Silicon MBE grown 250 nm epitaial Si P doped: at/cm 3 Tunnel barrier Al deposition and oidation APL 91, (2007) APL 98, (2011)

12 Outline Introduction to spin injection into silicon Spin injection into silicon at room temperature Inverted Hanle effect Control of spin polarization in Silicon 2DEG

13 Electrical creation of spin polarization in silicon at room temperature Spin injection and detection by single contact I V L >> L SD FM TB Silicon Spin Injection Manipulation Dt Detectionti Room Temperature n- and p- type Si

14 Ferromagnet/ Al 2 O 3 / Si interfaces Ni 80 Fe 20 Al 2 O 3 Silicon H- terminated Si (HF etched) Al 2O 3 : e-beam evaporation + Plasma oidation FM : e-beam evaporation 2 nm Sharp Ferromagnet/Tunnel barrier/si interfaces

15 Narrow Schottky barrier (FM/Al 2 O 3 /n ++ Si) Heavily doped Si Tunnel barrier Injection Φ B ~ 0.7 ev ity (A/m 2 ) K 5 K V E c Current densi FM n ++ Si W D ~ 5 nm E V V Si - V FM (V) (Tunneling regime) Tunneling behavior Efficient spin injection is possible

16 Electrical creation of spin polarization in n-si Spin injection Injection of spin-polarized electrons into Si through tunnel barrier Accumulation of spin-polarized electrons in conduction band of Si Creation of a spin splitting in conduction band ( μ)

17 Spin precession Spin precession in presence of transverse magnetic field B Spin Perpendicular B Larmor Frequency L g B B

18 Hanle effect Precession and depolarization of spins in transverse magnetic field Spin-signal has a Lorentzian line-shape (B) (0) 1 s ( L. ) 2 The half width is inversely proportional to the spin-lifetime

19 Hanle-signal in n-si at room temperature Ni 80 Fe 20 /Al 2 O 3 /n ++ Si mv V (mv) As doped, n = cm B (Oe) S. P. Dash et al. Nature 462, 491 (2009)

20 Spin accumulation ( ) V (mv) = 1.2 mev B (Oe) 2( V ) TSP Tunnel spin polarization (~ 30 %) =12meV 1.2 Spin-RA = (V / I). Area = 6 kωμm 2 S. P. Dash et al. Nature 462, 491 (2009)

21 Modeling the Hanle curves: Drift diffusion model d t S S t S D t S v t t S ), ( ) ( ), ( ), ( ), ( 2 2 Drift Diffusion Precession Dephasing s t v = Drift velocity v d = Drift velocity D = Diffusion τ s = Spin life time ω = Larmor frequency ω Larmor frequency Perpendicular B

22 Modeling the Hanle curves: Drift diffusion model d t S S t S D t S v t t S ), ( ) ( ), ( ), ( ), ( 2 2 Drift Diffusion Precession Dephasing s t Drift can be neglected in heavily doped Si Assume No diffusion Stationary spin-accumulation 2 ) ( 1 (0) (B) Perpendicular B ). ( 1 s L

23 Spin-life time and spin-diffusion length V (mv) (B) B (0) 1 (. ) Lorentzian fit L s = 142 ps Spin dephasing time (T * 2* ) S 1 L g B (HWHM ) = 142 ps B (Oe) Spin diffusion length = 230 nm S. P. Dash et al. Nature 462, 491 (2009)

24 Spin-signal with electrical bias (mv) V = 2.9 mev P Silicon = 4.6% K I (ma) The spin-signal increases linearly with current RA (km m 2 ) Spin V < 0 e e V > 0 1 spin etraction spin injection T = 300 K V Si - V FM (V) Spin-RA = (V / I). area Injection is more efficient than etraction S. P. Dash et al. Nature 462, 491 (2009)

25 Control eperiment to prove spin-polarized polarized tunneling Yb Au FM Non-magnetic Al 2 O 3 n-si V (mv) Ni 80 Fe 20 Ni 80 Fe Yb/Ni 80 Fe 20 Au/Ni 80 Fe V (mv) Non-magnetic nanolayer kill the spin polarization Presence of FM retain its associated effects B(Oe) B(Oe) No spin-accumulation induced in the silicon Zero Hanle spin-signal S. P. Dash et al. Nature 462, 491 (2009)

26 Spin polarization in p-si Ni 80 Fe 20 /Al 2 O 3 /p-si 10 5 Injection density (A/m 2 ) Current B doped = cm V Si - V FM (V) Injection of spin-polarized holes into p-si through tunnel barrier Accumulation of spin-polarized holes in valence band Creation of a spin splitting in valence band

27 Spin-signal due to Hanle effect in p-si Ni 80 Fe 20 /Al 2 O 3 /p-si -172 mv, 300K 0.0 μ = Spin life time (mv) V Lorentzian fit = 270 ps τ = 270 ps Si Spin diffusion i length = 310 nm B (Oe) μ S. P. Dash et al. Nature 462, 491 (2009)

28 Control eperiment to prove spin-polarized polarized tunneling in p-si FM Non-magnetic Al 2 O 3 p-si V (mv V) Au/Ni 80 Fe 20 Ni 80 Fe Non-magnetic nanolayer -0.6 kill the spin polarization B (Oe) Presence of FM retain its associated effects No spin-accumulation induced in the silicon Zero Hanle spin-signal

29 Spin-signal with electrical bias for p-si 0.0 Injection etraction 10 2 Injection Etraction V V (mv) 2 ) I (ma) A (km Spin-RA VSi -VFM (V) The spin-signal increases linearly with current Spin-RA = (V / I). area Injection is more efficient i than etraction S. P. Dash et al. Nature 462, 491 (2009)

30 Spin-signal with bias voltage -comparison km 2 ) Sp pin-ra (k 10 2 hl hole ij injection electron etraction electron injection V Si -V FM (V) hole etraction Injection is more efficient than etraction S. P. Dash et al. Nature 462, 491 (2009)

31 Outline Introduction to spin injection into silicon Spin injection into silicon at room temperature Inverted Hanle effect Control of spin polarization in Silicon 2DEG

32 Spin precession and depolarization with stray field yf d t S S t S D t S v t t S ), ( ) ( ), ( ), ( ), ( 2 2 Drift Diffusion Precession Dephasing s t

33 Inverted Hanle effect n-type Silicon Ni Ni 80 Fe 20 Co Fe S.P. Dash et al. PRB 84, (2011)

34 Spin precession and decoherence near an interface with a ferromagnet f f g n-type Silicon effec ctive = 1/ HWHM (ps) T= 300 K p-type Si n-type Si Ni Ni 80 Fe 20 Co Fe Saturation magnetization of ferromagnet (T) S.P. Dash et al. PRB 84, (2011)

35 Outline Introduction to spin injection into silicon Spin injection into silicon at room temperature Inverted Hanle effect Control of spin polarization in Silicon 2DEG

36 Formation of a 2 DEG K (MΩ -1 ) di/dv FM Gd Cs V FM Formation of 2DEG at Si/Al 2 O 3 interface by use of Low work function ferromagnet et Gd Cs for pinning of fermi level Jansen, Min, Dash, Nature mat. 9, 133 (2010)

37 Formation of a 2 DEG FM Gd Cs Jansen, Min, Dash, Nature mat. 9, 133 (2010)

38 Zeeman splitting of a Si 2DEG Application of magnetic field create Zeeman spin splitting of the energy levels in the Si 2DEG Electric field from the metal electrode modifies the relative position of Si Fermi level w.r.t spin split 2DEG sub band. This gives rise the spin polarization (100 % or 0%) in the Si 2DEG

39 Oscillatory spin-polarized tunneling from silicon quantum wells controlled by electric field Electrostatic modification of the magnitude of spin polarization in a Si 2DEG Detection by means of tunneling to a ferromagnet, producing prominent oscillations of tunnel magnetoresistance of up to 8%. Jansen, Min, Dash, Nature mat. 9, 133 (2010)

40 TMR with Magnetic field and Temperature Magnetic field Temperature B= 9 T Jansen, Min, Dash, Nature mat. 9, 133 (2010)

41 Amplitude of TMR with Zeeman Splitting Jansen, Min, Dash, Nature mat. 9, 133 (2010)

42 Summary Electrical creation of spin polarization in silicon at room temperature V > 0 e S. P. Dash et al. Nature 462, 491 (2009) Oscillatory spin polarized tunneling in a Si 2DEG R. Jansen, B. C. Min, S. P. Dash, Nature materials 9, 133 (2010)