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Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions Tomáš Jungwirth University of Nottingham Bryan Gallagher, Tom Foxon, Richard.

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Presentation on theme: "Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions Tomáš Jungwirth University of Nottingham Bryan Gallagher, Tom Foxon, Richard."— Presentation transcript:

1 Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions Tomáš Jungwirth University of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, et al. Hitachi & Univ. Cambridge Andrew Irvine, David Williams, Elisa de Ranieri, Byonguk Park, Sam Owen, et al. Institute of Physics ASCR Vít Novák, Kamil Olejník, Miroslav Cukr, Jorg Wunderlich, Alexander Shick, Karel Výborný, Jan Zemen, Jan Mašek, Josef Kudrnovský, František Máca, Jairo Sinova, Zdeněk Výborný, Vlastimil Jurka, Karel Hruška, et al. University of Texas Allan MacDonald et al.

2 Outline 1. Ferromagnetic semiconductor spintronics (GaMnAs) - ferromagnet like Fe,Ni,… singular d  /dT at T c - semiconductor like GaAs:C p-n junction transistor 2. Non-magnetic semiconductor spintronics - spin detection via spin-injection Hall effect - spin-photovoltaic p-n junction cell Ni GaMnAs

3 Ferromagnetic semiconductor (Ga,Mn)As EFEF DOS Energy spin  spin  << 1% Mn ~1% Mn >2% Mn onset of ferromagnetism near MIT Very dilute and random moments  compare with dense&ordered Fe, Ni,.. Very heavily doped semiconductor  compare with GaAs:C MIT at 0.01%C

4 Critical behavior of resistivity near T c Ordered magnetic semiconductors Disordered DMSs Sharp critical behavior of resistivity at T c Broad peak near T c and disappeares in annealed optimized materials Eu  chalcogenides

5 Fisher&Langer, PRL‘68 singular Nickel Scattering off correlated spin-fluctuations singular Eu 0.95 Gd 0.05 S

6 Fisher&Langer, PRL‘68 singular Nickel Scattering off correlated spin-fluctuations singular Eu 0.95 Gd 0.05 S

7 Fisher&Langer, PRL‘68 singular Nickel Scattering off correlated spin-fluctuations singular GaMnAs Eu 0.95 Gd 0.05 S Novak et al., PRL‘08

8 Optimized materials with upto ~8% Mn Ga and T c upto ~190 K

9 Optimized (Ga,Mn)As materials  well behaved itinerant ferromagnets resembling Fe, Ni, …. Annealing sequence of a 8% Mn Ga material Optimized materials with upto ~8% Mn Ga and T c upto ~190 K

10 Low-voltage gating of the highly doped GaAs:Mn Conventional MOS FET: ~ Volts Ohno et al. Nature ’00, APL ‘06 All-semiconductor p-n junction FET Owen, et al. New J. Phys.‘09 dpdp dpdp E gap VGVG p n p n Significant depletion in 5-10 nm (Ga,Mn)As at V G ~ E gap ~1 Volts

11 Low-voltage gating of the highly doped GaAs:Mn Conventional MOS FET: ~ Volts Ohno et al. Nature ’00, APL ‘06 Significant depletion in 5-10 nm (Ga,Mn)As at V G ~ E gap ~1 Volts 2x cm -3 All-semiconductor p-n junction FET Owen, et al. New J. Phys.‘09 Numerical simulations

12 Low-V tunable coercivity Switching by short low-V pulses Low-V accummulation/depletion (Ga,Mn)As p-n junction spintronic transistor

13 Zener kinetic-exchange (Ga,Mn)As SC with ~8%Mn Ga  T c  190 K compare with Stoner MnAs metal with 100%Mn Ga  T c  300 K  T c in (Ga,Mn)As in fact remarkable large T c ‘s 8%Mn Ga 0%Mn Ga Edmonds et al. APL‘08  Other semiconductor hosts, e.g. Li(Zn,Mn)As Mn Zn isovalent  no doping limit & independent control of carrier and moment concentrations  Proximity effects in FS/FM hybrids Magnetic behavior of a (Ga,Mn)As interfacial layer at room-T Masek et al., PRL‘07 Maccherozzi et al., PRL‘08 1 st part summary remarks

14  Low-V gating of GaMnAs by ferroelectric gate A superhybrid ferromagnetic/ferroelectric/semiconductin FET Stolichnov et al., Nature Materials ‘08 Maruyama et al., Nature Nanotechnology ‘08  Electrical gate control of ultra-thin Fe on Au 40% change of magnetic anisotropy by modest electric fields at room-T

15 2. Non-magnetic semiconductor spintronics - spin detection via spin-injection Hall effect - spin-photovoltaic p-n junction cell Ni GaMnAs 1. FM SC spintronics (GaMnAs) Summary  singular d  /dT at T c  very well behaved itinerant FM  p-n junction transistor controlled by ~1V fields  high-speed SC (opto-) spintronics

16 Spin-detection in semiconductors Ohno et al. Nature’99, others  Magneto-optical imaging  non-destructive  lacks nano-scale resolution and only an optical lab tool  MR Ferromagnet  electrical  destructive and requires semiconductor/magnet hybrid design & B-field to orient the FM  spin-LED  all-semiconductor  destructive and requires further conversion of emitted light to electrical signal Datta-Das transistor

17 Spin-detection in semiconductors Ohno et al. Nature’99, others Crooker et al. JAP’07, others  Magneto-optical imaging  non-destructive  lacks nano-scale resolution and only an optical lab tool  MR Ferromagnet  electrical  destructive and requires semiconductor/magnet hybrid design & B-field to orient the FM  spin-LED  all-semiconductor  destructive and requires further conversion of emitted light to electrical signal

18  Spin-injection Hall effect  non-destructive  electrical  nm resolution with current lithography  in situ directly along the SC channel (all-SC requiring no magnetic elements in the structure or B-field) Wunderlich et al. arXives:

19 Family of spintronic Hall effects (induced by spin-orbit coupling)

20 – – – – – – – – jqsjqs nonmagnetic Spin-polarizer (e.g. ferromagnet,  light) Spin injection Hall effect (SIHE) SIHE: spatially dependent unlike AHE in uniformly polarized systems Family of spintronic Hall effects (induced by spin-orbit coupling)

21 – – – – – – – – – – – jqsjqs nonmagnetic Spin-polarizer (e.g. ferromagnet,  light) Spin injection Hall effect (SIHE) SIHE: spin-polarized charge current unlike (i)SHE Family of spintronic Hall effects (induced by spin-orbit coupling)

22 22 i p n 2DHG Optical injection of spin-polarized charge currents into Hall bars  GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell

23 - 2DHG i p n 23 Optical injection of spin-polarized charge currents into Hall bars  GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell

24 i p n 2DHG 2DEG 24 Optical injection of spin-polarized charge currents into Hall bars  GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell

25 2DHG 2DEG e h e e ee e h h h h h VHVH 25 Optical injection of spin-polarized charge currents into Hall bars  GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell

26 Optical spin-generation area near the p-n junction Simulated band-profile p-n junction bulit-in potential (depletion length ) ~ 100 nm  self-focusing of the generation area of counter-propagating e - and h + Hall probes further than 1  m from the p-n junction  safely outside the spin-generation area

27 see also Bernevig et al., PRL‘06 Spin-diffusion along the channel of injected spin-  electrons Spin-charge dynamics in disordered 2DEG with in-plane Rashba (  ) / Dresselhaus (  ) spin-orbit fields SO-length (~1  m)

28 see also Bernevig et al., PRL‘06 Spin-diffusion along the channel of injected spin-  electrons Local spin-dependent transverse deflection due to skew scattering ~10nm Spin-charge dynamics in disordered 2DEG with in-plane Rashba (  ) / Dresselhaus (  ) spin-orbit fields SO-length (~1  m) >> mean-free-path (~10 nm)

29 SIHE device realization n3,n2,n1: local SIHE n0: averaged-SIHE / AHE Spin-generation area

30 -- V sd = 0V SIHE detection at n2 R Hall [  ] ++

31 n1n2 Linear in the degree of circular polarization of light  spin-polarization of injected el.

32 SIHE survives to high temperatures -- ++

33 SIHE angle ~ & +/- alternating on a  m scale, all as expected from theory -- ++ n0 n1 n2 n3  H [10 -3 ] x [  m]

34 2 nd part. summary remarks  Spin-photovoltaic cell: polarimeter on a SC chip requiring no magnetic elements, external magnetic field, or bias; form IR to visible light depending on the SC  Spin-detection tool for other device concepts (e.g. Datta-Das transistor)  Basic studies of quantum-relativistic spin-charge dynamics also in the intriguing and more controversial strong SO regime in archetypal 2DEG systems

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