Spintronic device structures

Transcription

1 Spintech V Krakow Spintronic device structures Jaroslav Fabian Institute for Theoretical Physics University of Regensburg

2 Giant Magnetoresistance (GMR) magnetoelectronics Tunneling Magnetoresistance (TMR) F I F Julliere 1975; Moodera et al Grunberg; Fert (1988) "for the discovery of giant magnetoresistance" applications: HDD, MRAM

3 :outline: what can we do with (ensemble) spin in semiconductors road map issues: injection, detection, relaxation spin transistors bipolar spintronic devices magnetic resonant tunneling diodes closing I. Zutic, J. Fabian, and S. Das Sarma, Spintronics: Fundamentals and applications, Rev. Mod. Phys. 76, 323 (2004) J. Fabian, A. Matos-Abiague, C. Ertler, P. Stano, and I. Zutic, Semiconductor spintronics, Acta Physica Slovaca, 57, (2007)

4 spintronics drive technology fundamental discoveries

5 SPINTRONICS GOALS spin control of electrical properties (I-V characteristics) electrical control of spin (magnetization)

6 :semiconductor spintronics devices: spin something spin Zener diodes spin resonant diodes spin field-effect transistors magnetic semiconductor tunnel junction devices magnetic unipolar and bipolar junction diodes and transistors spin optoelectronic devices spin galvanics devices spin Hall polarizers spin-polarized semiconductor lasers spin pumping batteries spin-torque devices spin ratchets spin memrams spin quantum computers...

7 International Technology Roadmap 2004 for Semiconductors: Emerging Research Logic Devices RSFQ 1-D structures resonant tunneling SET molecular QCA spin transistor risk 2005, 2006

8 International Technology Roadmap 2004 for Semiconductors: Emerging Research Logic Devices RSFQ 1-D structures resonant tunneling SET molecular QCA spin transistor risk 2007, 2008

9 Intl. Technol. Roadmap for Semiconductor will we have a useful spin transistor?

10 SPINTRONICS 3 REQUIREMENTS EFFICIENT SPIN INJECTION (slow) SPIN (efficient) SPIN CONTROL F N spin accumulation RELIABLE SPIN DETECTION Silsbee-Johnson spin-charge coupling

11 :spin injection: made visible S. A. Crooker et al., JAP, 101, (2007) S. A. Crooker at al., Science 309, 2191 (2005)

12 :spin injection: all-semiconductor all-electrical spin injection/detection z x/[010] -y/[100] non-local spin injection/detection device 1 I inj V V V L magnetic Esaki diode contacts Au/Ti (Ga,Mn)As n + -GaAs n + n-gaas n-gaas vb cb Spin injection P inj 50% M. Ciorga et al., PRB 79, (2009); see poster 161

13 Silsbee-Johnson spin-charge coupling R. H. Silsbee, Bull. Magn. Reson.2, 284 (1980); M. Johnson and R. H. Silsbee, Phys. Rev. Lett. 55, 1790 (1985) spin accumulation Q: Suppose there is a source of nonequilibrium spin accumulation at the far right of N. What is the emf due to the proximity with the equilibrium spin polarization P j in F? J. Fabian and I. Zutic, The standard model of spin injection, in book From GMR to Quantum Information, (Forschungszentrums Juelich, 2009), Eds. S. Blügel et al; also in arxiv:

14 :spin relaxation: GaAs, Si GaAs (low temperature) Si (non-degenerate densities) see also poster 264 (Jiang and Wu) J. L. Chang, M. W. Wu, and J. Fabian, arxiv:

15 :spin relaxation: persistent spin helix: engineering spin lifetime Theory: B. A. Bernevig, J. O. Orenstein, and S. C. Zhang, Phys. Rev. Lett. 97, (2006). Experiment: J. D. Koralek, C. P. Weber, J O. Orenstein, B. A. Bernevig, S. Z. Zhang, S. Mack, D. D. Awschalom, Nature, 458, 610 (2009). individual spin components: short spin lifetime spin helix: 100-times longer spin lifetime From J. Fabian, Nature (N&V) 458, 580 (2009) increased spin injection efficiency J. L. Cheng, M. W. Wu,, and I. C. da Cunha Lima, Phys. Phys. B 75, (2007)

16 :materials issues: room temperature ferromagnetic semiconductors? GaMnAs Fe/GaMnAs (Ga,Mn)As Fe Au T. Jungwirth et al., Rev. Mod. Phys. 78, 809 (2006) F. Maccherozzi et al., Phys. Rev. Lett. 101, (2008) See also poster 234 for related work S. Mark et al % Mn p-doped (Mn replaces Ga) degenerate: p = /cm 3 Tc up to 180 K fm and p-density coupled impurity band or not? above room-temperature fm a few nm of GaMnAs involved bias control? anisotropies?

17 intl. Semiconductor roadmap 2007 emerging research logic devices

18 :spin transistors: Datta-Das Sugahara-Tanaka Johnson hot-electron spin transistors Magnetic bipolar transistor J. Fabian, A. Matos-Abiague, C. Ertler, P. Stano, and I. Zutic, Semiconductor spintronics, Acta Phys. Slov, 57, 566 (2007)

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20 Bipolar spintronic devices with I. Zutic and S. Das Sarma he is bipolar Spin-polarized pn junction diode, spin capacitance I. Zutic, J. Fabian and S. Das Sarma, Phys. Rev. B 64, (2001) Spin-polarized solar cell I. Zutic, J. Fabian and S. Das Sarma, Appl. Phys. Lett. 79, 1558 (2001) Magnetic bipolar diode (MBD), GMR, spinvoltaic effect, spin injection, spin extraction I. Zutic, J. Fabian and S. Das Sarma, Phys. Rev. Lett. 88, (2002) General theory of magnetic bipolar devices J. Fabian. I. Zutic, and S. Das Sarma, Phys. Rev. B 66, (2002) Magnetic bipolar transistor (MBT), magnetoamplification J. Fabian, I. Zutic, and S. Das Sarma, cond-mat/ ; Appl. Phys. Lett. 84, 85 (2004) J. Fabian and I. Zutic, Phys. Rev. B 69, (2004); Appl. Phys. Lett. (2005) Spin injection into silicon: bipolar mode I. Zutic, J. Fabian, and S. Erwin, Phys. Rev. Lett. 97, (2006)

21 Bipolar spintronic devices with I. Zutic and S. Das Sarma he is bipolar Spin-polarized pn junction diode, spin capacitance I. Zutic, J. Fabian and S. Das Sarma, Phys. Rev. B 64, (2001) Spin-polarized solar cell I. Zutic, J. Fabian and S. Das Sarma, Appl. Phys. Lett. 79, 1558 (2001) Magnetic bipolar diode (MBD), GMR, spinvoltaic effect, spin injection, spin extraction I. Zutic, J. Fabian and S. Das Sarma, Phys. Rev. Lett. 88, (2002) General theory of magnetic bipolar devices J. Fabian. I. Zutic, and S. Das Sarma, Phys. Rev. B 66, (2002) Magnetic bipolar transistor (MBT), magnetoamplification J. Fabian, I. Zutic, and S. Das Sarma, cond-mat/ ; Appl. Phys. Lett. 84, 85 (2004) J. Fabian and I. Zutic, Phys. Rev. B 69, (2004); Appl. Phys. Lett. (2005) Spin injection into silicon: bipolar mode I. Zutic, J. Fabian, and S. Erwin, Phys. Rev. Lett. 97, (2006)

22 CONVENTIONAL DIODE 101

23 ratchet and paw analog of a pn junction diode generation current recombination current p n

24 :magnetic diode: spin-voltaic effect: spin-charge coupling

25 GiantMagnetoResistance in MDs Spin-charge coupling: proximity of equilibrium (P p ) and nonequilibrium (δp n )spin

26 what is in the numerics?

27 drift-diffusion n-collector n-emitter p-m-base think of Stern-Gerlach

28 charge and spin continuity spin relaxation

29 self-consistency with electrostatics

30 :analytical modeling: generalized Shockley theory J. Fabian, I. Zutic, S. Das Sarma, Phys. Rev. B 66, (2002) carrier and spin quasiequilibrium in space-charge regions (constant spin-resolved chemical potentials) + continuity of spin current through space-charge regions

31 :magnetic pn junctions: qualitative statements Impossibility of spin injection at low biases Spin injection of nonequilibrium spin only (beyond the standard spin injection model) Spin-charge coupling Magnetic pn junction arrays (matrix theory): J. Fabian, A. Matos-Abiague, C. Ertler, and P. Stano, Semiconductor spintronics, Acta Phys. Slov, 57, 566 (2007)

32 experimental observation of spin-voltaic effect in a paramagnetic pn junction T. Kondo, J. Hayafuji, and H. Munekata, Investigation of spin-voltaic effect in a p-n heterojunctions, Jpn. J. Appl. Phys. 45, L663 (2006)

33 experimental observation of spin-voltaic effect in a ferromagnetic pn junction P. Chen, J. Moser, P. Kotissek, J. Sadowski, M. Zenger, D. Weiss, and W. Wegscheider All electrical measurement of spin injection in a magnetic p-n junction diode, Phys. Rev. B 74, (R) (2006)

34 :spin-injection Hall effect: spin-polarized pn junction & local extraordinary Hall transport J. Wunderlich et al, Nature Phys. (in press); arxiv: (see poster 288) Local ( nm) nondistructive electric measurement of spin polarization high-temperature (200 K) operation probe of fundamental spin-orbit (spin helix) physics

35 bipolar junction transistor microphone e emitter base e collector e ultra high speed digital circuits small-signal amplification high frequency analog circuits (SiGe, GaAs HBTs) integrated Circuits market: 20% BJT, 75% MOSFET

36 :magnetic bipolar transistor (MBT): J. Fabian, I. Zutic and S. Das Sarma, cond-mat/ (2002); Appl. Phys. Lett. 84, 85 (2004); J. Fabian and I. Zutic, Phys. Rev. B 69, (2004). M. Flatte, Z. G. Yu, E. Johnston-Halperin, and D. D. Awschalom, Appl. Phys. Lett. 82, 4740 (2003) N. Lebedeva and P. Kuivalainen, J. Appl. Phys. 93, 9845 (2003) all semiconductor magnetic semiconductor active region versatile design materials restricted

37 :spin-polarized bipolar lasers: reducing the threshold power optical injection of spin-polarized carriers provides a threshold current reduction for the lasing operation J. Rudolph et al., APL 87, (2005); 82, 4516 (2003) electrical spin injection threshold reduction M. Holub et al., PRL 98, (2007) Limited theoretical understanding Threshold strongly depends on the recombination mechanism Maximum threshold reduction larger than previously thought possible Very short spin relaxation time of holes is advantageous C. Gothgen, R. Oszwaldowski, A. Petrou, I. Zutic, APL 93, (2008) I. Vurgaftman et al., APL 93, (2008)

38 Magnetic Resonant Tunnel Diodes A. Slobodskyy et al, Phys. Rev. Lett. 90, (2003) C. Ertler and J. Fabian, Appl. Phys. Lett. 89, (2006) C. Ertler and J. Fabian, Phys. Rev. B (2007) ZnSe ZnSe BeZnSe BeZnSe ZnMnSe ZnMnSe b) ZnSe ZnSe Current (0-150 μa) 8% Mn T=1.3K B 0T 3T 6T 1.3 K a) Voltage (0-0.2 V) efficient spin filtering spin detection fast switching times coherence issues RT operation? see posters , 176, 177, 181, 219, 242, 284 Current Density (A/cm 2 ) x 105 T = 4.2 K Energy (mev) 100 out ΔV z (nm) 0 out 0 ΔV Voltage (V) 50 Δ E = 0 Δ E = 5 mev Δ E = 10 mev Δ E = 15 mev Δ E = 20 mev Δ E = 25 mev Δ E = 40 mev ΔV 3 out

39 V in :Digital Magneto Resistance (DMR): Ertler and Fabian, Appl. Phys. Lett. 89, (2006) mono-to-bistable logic element (mobile) (multi-valued logic roadmap, up to 100 GHz demo) Maezawa and Mizutani, Jpn. J. Appl. Phys. 32, L42 (1993) load I driver Load RTD V in V in V out mono V out low B V load = V in V out, I load =I driver Driver mrtd mono high

40 operational principle of DMR C. Ertler and J. Fabian, Appl. Phys. Lett. 89, (2006); Phys. Rev. B 75, (2007) V in RTD V in V out B threshold mrtd B V out low high high mono mono mono mono

41 :self-sustained magneto-electric oscillations in MRTDs: C. Ertler and J. Fabian, Phys. Rev. Lett. 101, (2008) ; poster 168 see also poster 169, Carretero et al. for related work Non-linear coupling of charge, magnetization, and current leads to temporal oscillations of the current etc under dc bias (a) x j max (b) 20 j (a.u.) (c) j (a.u.) 10 5 I j min Voltage (mv) x II j tot j j Time (t*) Δ (mev) (d) n (1/cm 2 ) I Δ max Δ min Voltage (mv) 14 x Time (t*) II n tot n n

42 Intl. Technol. Roadmap for Semiconductor will we have a useful spin transistor?

43 Intl. Technol. Roadmap for Semiconductor will we have a useful spin transistor? too early to say

44 :conclusions: demonstrate spintronic device schemes new fm materials/materials combinations new physical principles for spin-based devices involve electrical engineers SFB 689 DFG Collaborative Research Center (Regensburg) Spin phenomena in reduced dimensions SPP 1285 DFG Priority Program Semiconductor Spintronics