Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions

1. Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions Tomáš Jungwirth Hitachi & Univ. Cambridge Andrew Irvine, David Williams, Elisa de Ranieri, Byonguk Park, Sam Owen, etal. University of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, 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 Tc - semiconductor like GaAs:C p-n junction transistor Ni GaMnAs 2. Non-magnetic semiconductor spintronics - spin detection via spin-injection Hall effect - spin-photovoltaic p-n junction cell

3. EF spin  ~1% Mn << 1% Mn >2% Mn DOS Energy spin  onset of ferromagnetism near MIT Ferromagnetic semiconductor (Ga,Mn)As • 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 Tc Ordered magnetic semiconductors Disordered DMSs Eu chalcogenides Broad peak near Tc and disappeares in annealed optimized materials Sharp critical behavior of resistivity at Tc

5. singular singular Scattering off correlated spin-fluctuations Fisher&Langer, PRL‘68 Eu0.95Gd0.05S Nickel

6. singular singular Scattering off correlated spin-fluctuations Fisher&Langer, PRL‘68 Eu0.95Gd0.05S Nickel

7. singular singular Scattering off correlated spin-fluctuations Fisher&Langer, PRL‘68 Eu0.95Gd0.05S GaMnAs Nickel Novak et al., PRL‘08

8. Optimized materials with upto ~8% MnGa and Tc upto ~190 K

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

10. p n p n VG Egap dp dp Low-voltage gating of the highly doped GaAs:Mn Conventional MOS FET: ~10-100 Volts Ohno et al. Nature ’00, APL ‘06 All-semiconductor p-n junction FETOwen, et al. New J. Phys.‘09 Significant depletion in 5-10 nm (Ga,Mn)As at VG ~ Egap ~1 Volts

11. Low-voltage gating of the highly doped GaAs:Mn Conventional MOS FET: ~10-100 Volts Ohno et al. Nature ’00, APL ‘06 All-semiconductor p-n junction FETOwen, et al. New J. Phys.‘09 Numerical simulations 2x 1019 cm-3 Significant depletion in 5-10 nm (Ga,Mn)As at VG ~ Egap ~1 Volts

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

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

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

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

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

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

18. Spin-injection Hall effect  non-destructive  electrical  100-10nm 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:0811.3486

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

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

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

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

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

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

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

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

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

29. SIHE device realization n0: averaged-SIHE / AHE n3,n2,n1: local SIHE Spin-generation area 2 3 1 0

30. SIHE detection at n2 - RHall [] + Vsd= 0V 2 3 1 0

31. Linear in the degree of circular polarization of light  spin-polarization of injected el. n1 n2

32. SIHE survives to high temperatures - +

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

34. 2nd 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