Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions Tomas Jungwirth University of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, et al. Hitachi Cambridge, Univ. Cambridge Jorg Wunderlich, Andrew Irvine, David Williams, Elisa de Ranieri, Byonguk Park, Sam Owen, et al. Institute of Physics ASCR Vít Novák, Alexander Shick, Karel Výborný, Jan Masek, Josef Kudrnovsky, et al. Texas A&M, University of Texas Jairo Sinova, Allan MaDonald et al.

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 Ni GaMnAs

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

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

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

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

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

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

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

8%Mn Ga 0%Mn Ga 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 Below room-temperature T c in (Ga,Mn)As but in fact remarkable large T c ‘s Edmonds et al., APL‘08

MIT in p-type GaAs: - C (30meV) ~ cm -3 - Mn (110meV) ~10 20 cm -3 Mobilities in GaAs:Mn: x larger in GaAs:C - similar in GaAs:Mg Short-range p-d kinetic-exchange (hybridization) alone cannot bind the hole  same type of MIT (screening of long-range Coulomb) as with C, … but shifted to significantly higher dopings GaAs:Mn – a doped p-type semiconductor Mn-d local moments As-p holes

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. arXiv: 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

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. arXiv: Numerical simulations

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

Low-V controlled K c and K u magnetic anisotropies -1V+3 V Experiment Theory

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

2. Non-magnetic semiconductor spintronics - spin detection via spin-injection Hall effect - spin-photovoltaic p-n junction 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

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

 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:

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

– – – – – – – – – – – 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)

– – – – – – – – 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)

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

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

i p n 2DHG 2DEG 25 Optical injection of spin-polarized charge currents into Hall bars  GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell

2DHG 2DEG e h e e ee e h h h h h VHVH 26 Optical injection of spin-polarized charge currents into Hall bars  GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell

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

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)

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)

Our 2DEG in the weak spin-orbit, strong scattering regime  non-controversial  Typical spin-orbit length in GaAs 2DEG ~  m  injected spins will rotate at  m scale  Hall effect in the diffusive regime dominated by skew-scattering  Hall angles ~10 -3 (comparable to AHE in FMs) In-plane SO field Diffusion of out-of-plane injected spins Skew-scattering off SO-imputity potential Corresponding Hall angle for a given out-of-plane polarization

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

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

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

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

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

2. Non-magnetic SC spintronics Summary  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

Ga As Mn -  h+ h+  h+ h+

Ga As Mn