Transcript Slide 1
Semiconductor spintronics in ferromagnetic and non-magnetic p-n junctions Tomas Jungwirth Institute of Physics ASCR Vít Novák, Alexander Shick, Karel Výborný, Jan Masek, Josef Kudrnovsky, et al. Hitachi Cambridge, Univ. Cambridge University of Nottingham Bryan Gallagher, Tom Foxon, Richard Campion, Kevin Edmonds, Andrew Rushforth, et al. Texas A&M, University of Texas Jorg Wunderlich, Andrew Irvine, David Williams, Jairo Sinova, Allan MaDonald et al. Elisa de Ranieri, Byonguk Park, Sam Owen, et al. Outline 1. Ferromagnetic semiconductor spintronics (GaMnAs) - ferromagnet like Fe,Ni,… singular d/dT at Tc - 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 DOS spin << 1% Mn EF ~1% Mn >2% Mn Energy spin Very dilute and random moments compare with dense&ordered Fe, Ni,.. onset of ferromagnetism near MIT Very heavily doped semiconductor compare with GaAs:C MIT at 0.01%C Critical behavior of resistivity near Tc Ordered magnetic semiconductors Disordered DMSs Eu chalcogenides Sharp critical behavior of resistivity at Tc Broad peak near Tc and disappeares in annealed optimized materials Scattering off correlated spin-fluctuations (T ) ~ Si S0 Si S0 singular (F d ) ~ Fisher&Langer, PRL‘68 Eu0.95Gd0.05S Nickel (F ~ d ) ~ U singular d / dT ~ dU / dT cv Scattering off correlated spin-fluctuations (T ) ~ Si S0 Si S0 singular (F d ) ~ Fisher&Langer, PRL‘68 Eu0.95Gd0.05S Nickel (F ~ d ) ~ U singular d / dT ~ dU / dT cv Scattering off correlated spin-fluctuations (T ) ~ Si S0 Si S0 singular (F d ) ~ Eu0.95Gd0.05S Fisher&Langer, PRL‘68 GaMnAs Nickel (F ~ d ) ~ U singular d / dT ~ dU / dT cv Novak et al., PRL ‚08 Optimized materials with upto ~8% MnGa and Tc upto ~190 K 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, …. Edmonds et al., APL‘08 0%MnGa 8%MnGa Below room-temperature Tc in (Ga,Mn)As but in fact remarkable large Tc ‘s Zener kinetic-exchange (Ga,Mn)As SC compare with Stoner MnAs with ~8%MnGa Tc 190 K metal with 100%MnGa Tc 300 K GaAs:Mn – a doped p-type semiconductor Mobilities in GaAs:Mn: - 3-10x larger in GaAs:C - similar in GaAs:Mg MIT in p-type GaAs: - C (30meV) ~ 1018 cm-3 - Mn (110meV) ~1020 cm-3 Short-range p-d kinetic-exchange (hybridization) alone cannot bind the hole Mn-d local moments As-p holes same type of MIT (screening of long-range Coulomb) as with C, … but shifted to significantly higher dopings 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 FET Owen, et al. arXiv:0807.0906 p n p Egap n VG dp d p [2 n( Egap VG ) p(n p) ]1/ 2 ~ nm's d p Significant depletion in 5-10 nm (Ga,Mn)As at VG ~ Egap ~1 Volts 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 FET Owen, et al. arXiv:0807.0906 Numerical simulations 2x 1019 cm-3 Significant depletion in 5-10 nm (Ga,Mn)As at VG ~ Egap ~1 Volts Low-V accummulation/depletion Low-V tunable coercivity Switching by short low-V pulses (Ga,Mn)As p-n junction spintronic transistor Low-V controlled Kc and Ku magnetic anisotropies -1V +3 V Experiment Theory 1. FM SC spintronics (GaMnAs) Summary Ni singular d/dT at Tc very well behaved itinerant FM p-n junction transistor controlled by ~1V fields high-speed SC (opto-) spintronics GaMnAs 1. FM SC spintronics (GaMnAs) Summary Ni singular d/dT at Tc 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 GaMnAs Spin-detection in semiconductors 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 Ohno et al. Nature’99, others 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 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 Family of spintronic Hall effects (induced by spin-orbit coupling) AHE iSHE ++++++++++ ––––––––––– Ferromagnetic (polarized charge current) ++++++++++ jqs ––––––––––– nonmagnetic (pure spin current) js Family of spintronic Hall effects (induced by spin-orbit coupling) AHE iSHE ++++++++++ ––––––––––– ++++++++++ jqs ––––––––––– nonmagnetic (pure spin current) Ferromagnetic (polarized charge current) Spin injection Hall effect (SIHE) ++++++++++ ––––––––––– Spin-polarizer (e.g. ferromagnet , light) jqs nonmagnetic SIHE: spin-polarized charge current unlike (i)SHE js Family of spintronic Hall effects (induced by spin-orbit coupling) AHE iSHE ++++++++++ ––––––––––– ++++++++++ jqs ––––––––––– nonmagnetic (pure spin current) Ferromagnetic (polarized charge current) Spin injection Hall effect (SIHE) ++++ –––– –––– ++++ Spin-polarizer (e.g. ferromagnet, light) jqs nonmagnetic SIHE: spatially dependent unlike AHE in uniformly polarized systems js Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell ni p 2DHG 23 Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell - ni p 2DHG 24 Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell p i n 2DHG 2DEG 25 Optical injection of spin-polarized charge currents into Hall bars GaAs/AlGaAs planar 2DEG-2DHG photovoltaic cell h h h h h h e VH e e e e e 2DHG 2DEG 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 1m from the p-n junction safely outside the spin-generation area Spin-charge dynamics in disordered 2DEG with in-plane Rashba () / Dresselhaus () spin-orbit fields SO-length (~1m) Spin-diffusion along the channel of injected spin- electrons see also Bernevig et al., PRL‘06 Spin-charge dynamics in disordered 2DEG with in-plane Rashba () / Dresselhaus () spin-orbit fields SO-length (~1m) >> mean-free-path (~10 nm) Spin-diffusion along the channel of injected spin- electrons see also Bernevig et al., PRL‘06 Local spin-dependent transverse deflection due to skew scattering 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 In-plane SO field Diffusion of out-of-plane injected spins Hall effect in the diffusive regime dominated by skew-scattering Hall angles ~10-3 (comparable to AHE in FMs) Skew-scattering off SO-imputity potential Corresponding Hall angle for a given out-of-plane polarization SIHE device realization n3,n2,n1: local SIHE 3 2 1 0 n0: averaged-SIHE / AHE Spin-generation area SIHE detection at n2 RHall [] 50 - 25 0 -25 + Vsd= 0V -50 3 2 1 0 RL [k] 20 10 0 0 25 tm [s] 50 75 Linear in the degree of circular polarization of light spin-polarization of injected el. 2 10 5 n2 -3 H [ 10 ] n1 -3 H [ 10 ] 1 0 0 -5 -1 -10 -2 -1.0 -0.5 0.0 0.5 ( ) / ( ) 1.0 -1.0 -0.5 0.0 0.5 ( ) / ( ) 1.0 SIHE survives to high temperatures -3 H [10 ] 5 - 100K 160K (x2) 220K (x3) 0 -5 + 0 30 60 90 120 150 180 tm [s] SIHE angle ~ 10-3 & +/- alternating on a m scale, all as expected from theory n1 n2 n3 n0 10 n0 (x3) n2 - -3 H [10 ] 5 0 n1 (x3) n3 (x3) -5 -10 + 0 10 20 30 tm [s] 40 50 H [10-3] 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 Mn Ga h+ As Mn + h Ga Mn As