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Diluted Magnetic Semiconductors David Ferrand

Diluted Magnetic Semiconductors David Ferrand Equipe mixte CNRS-CEA-UJF “Nanophysique et semiconducteurs” Laboratoire de Spectrométrie Physique, BP 87 38402 Saint Martin d’Hères. Spin manipulation. Kroutvar et al., Nature 432 ,81 (2004). Injection and manipulation of spins in semiconductors.

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Diluted Magnetic Semiconductors David Ferrand

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  1. Diluted Magnetic Semiconductors David Ferrand Equipe mixte CNRS-CEA-UJF “Nanophysique et semiconducteurs” Laboratoire de Spectrométrie Physique, BP 87 38402 Saint Martin d’Hères

  2. Spin manipulation Kroutvar et al., Nature 432,81 (2004) Injection and manipulation of spins in semiconductors Electrical spin injection, spin transport, tunnel structure M. Kohda et al, Jpn. J. Appl. Phys., Part 2 40, L1274 (2001) R. Mattana et al, Phys Rev Lett, 90 166601 (2003)

  3. Outline I : Spins localized in II-VI heterostructures 1. Modulation doped heterostructures : II-VI Ferromagnetic quantum wells 2. CdTe quantum dots doped with a single Mn atom II : High band gap diluted magnetic semiconductors GaMnN/ZnCoO ZnCrTe 1. GaMnN, ZnCoO 2. ZnCrTe

  4. II-VI semimagnetic heterostructures Mn : 4s2 3d5 Isoelectronic element S=5/2 localized spins Magnetic alloys : Cd1-xMnxTe, Zn1-xMnxTe With a large Mn solubility up to 75% Almost perfect semiconducting properties II Cd0.7Mg0.3Te L CdTe Cd0.7Mg0.3Te Cd0.88Zn0.12Te substrate CdTe/CdMgTe quantum wells ZnTe CdTe CdTe ZnTe ZnTe substrate CdTe/ZnTe quantum dots

  5. J2, J3~0.5K kT << J1 N.N pairs J1~20K 0,0 0,1 0,2 0,3 0,4 0,5 0,05 0,05 J. Furdyna et al, JAP 64 R29 (1988) 0,04 0,04 0,03 0,03 0,02 0,02 0,01 0,01 xeff 0,00 0,00 0,0 0,1 0,2 0,3 0,4 0,5 Studies at low temperatures with diluted alloys Mn content x Small concentration of free spins Magnetic properties : Short range antiferromagnetic interactions a

  6. Surface doped CdMnTe QW 15 nm < z < 60 nm After surface oxydation W. Maslana, 2003 Mn Compositions 0-11% Hole densities 1-2 1011 cm-2 p type modulation doped CdMnTe QWs Magnetic quantum well Cd(1-x)MnxTe 80 Å spacer Barrier Substrate CdMgTe 2D hole gas Nitrogen E1 HH1 80 Å Mn Compositions 0-4% Hole densities 1-3 1011 cm-2

  7. b~-100 meV nm3 < 0 Holes : Electrons : a~25 meV nm3 > 0 HH -1 Excitons Xhh + B=+4 T HH +1 s+ s- N0~few 1022 cm-3 N0a~0.2 eV N0b~-1 eV - G.S T=1.9K Magneto-optical spectroscopy : Giant Zeeman effect ±1/2 E1 +1 z Photon -1 HH HH Excitons ±3/2

  8. Susceptibility PL at 2.1K, 2.4% Mn, 1.61011 cm-2 Haury et al, 1997 Interactions ferromagnétiques induite par le gaz 2D Tcw~-TAF=-2K < 0 Tcw ~ 2 à 3 K > 0 Susceptibility measurements : Curie Weiss temperature Coll. P. Kossacki, Warsaw

  9. V p doped QW undoped barriers n doped Electrical control through an electrostatic gate H. Boukari et al, Phys. Rev. Lett. 88, 207204 (2002) Tc depleted Hole gas

  10. 2D D.O.S Kossacki 2001 X 2.3 4% Mn Comparison with mean field model predictions Effective Mn content : xeff TC > TCW ? T. Dietl, Warsaw

  11. 3D-coherent islands h > hcSK "Stranski-Krastanow" Magnetic CdMnTe/ZnTe QDs • Strained induced CdTe/ZnTe QDs: • UHV-AFM image of CdTe QDs on ZnTe. QDs density: 1010 cm-2 Size: d=25nm, h=3nm (Lz<<Lx,Ly) • TEM C. Bougerol. Introduction of Mn atoms (3d5 4s2 ) carrying S=5/2 localized spin Thèse L Maingault, H. Mariette

  12. Single dot spectroscopy : • Strained induced Cd(Mn)Te/ZnTe QDs: 100mm • Mn segregation during the growth of a spacer layer Mn density = QDs density Thèse L Maingault, H. Mariette CdTe/ZnTe QDs doped with a single Mn atom Thèse Y. Léger

  13. Growth axis z s=1/2 B=0 Jz=±3/2 // Oz Electron : s=1/2 Anisotropic hole Jz=3/2 Reference CdTe/ZnTe QDs Reference CdTe/ZnTe QD : B=0 -1 +1 +1 ±1 -1 G.S. L. Besombes et al., Phys. Rev. Lett. 93, 207403 (2004)

  14. S=5/2 CdTe QDs with an individual Mn spin Individual Mn-doped CdTe/ZnTe QDs  Mn-doped CdTe/ZnTe QDs: 6 twofold degenerate excitonics levels Total splitting 1.3 meV Thèse Y. Léger

  15. 5 - ( I 3 I ) - - e Mn h Mn 2 Exciton-Mn Exchange Coupling S=5/2 Complexe X - Mn : s=1/2 + Jz=3/2 + S=5/2 Mn2+ e h e h -5/2 +5/2 Jz = -1 Jz = +1 X -3/2 +3/2 -1/2 +1/2 +1/2 -1/2 +3/2 -3/2 e h Jz = -1 e h +5/2 -5/2 Jz = +1 Overall splitting : • Ie-Mn=-70 meV and Ih-Mn =350 meV. Detection and manipulation of a single Mn spin

  16. Mn-Doped Individual QDs Under Magnetic Field • Splitting of the six exciton lines. • Diamagnetic shift. • Changes in the PL intensity distribution. • Large anticrossing for five of the exciton lines around 6T. • Additional tiny anticrossings. NMn=0 NMn=1

  17. II : High band gap diluted magnetic semiconductors GaMnN/ZnCoO 1. GaMnN, ZnCoO 2. ZnCrTe III-V Mn 4s2 3d5 Acceptor : GaMnAs 3d5 Isoelectronic : 3d4 II-VI : Cr2+ : 4s2 3d4 Co2+ : 4s2 3d7

  18. Towards room temperature diluted magnetic semiconductors ? 2001 (Ga,Mn)N 2002 MBE 3-6% Mn (Zn,Co)O :PLD 15-25% Co Tc>300K S. Sonoda et al. J.A.P. 156, 555 (2002) K. Ueda et al, APL 79 988 (2001) (Zn,Cr)Te MBE 0< x < 50% H. Saito et al, 2003 2003

  19. Partially filled d bands located within the gap ? Ferromagnetism mediated by electrons ? D.O.S e BV t2 BC BV e t2 BC E E e t2 Cr2+ in II-VI 3d4 3d7 Co2+ in ZnO Mn3+ in III-V High temperature ferromagnetism still controversial : • Paramagnetism + Ferromagnetism observed by SQUID ZnCrTe • No phase diagram with the magnetic ion composition • or correlation with other parameters - Transport properties weakly sensitive to magnetic ions Tunnel junctions with (Zn,Co)O • No sharp optical features close to band edges • No photoluminescence Diluted high band gap alloys : GaMnN, ZnCoO

  20. D.O.S e < 3d5 BV t2 BC E e t2 Zn1-xCoxO or Ga1-xMnxN c - axis WURTZITE epilayer Buffer • Grown by Molecular Beam Epitaxy: • in CREHA Valbonne (Zn1-xCoxO) • C. Deparis, C. Mohrhain • in Grenoble (Ga1-xMnxN) Al2O3 substrate

  21. (Zn,Co)O 2% Co Tetrahedral crystal field Spin forbidden transition at 1876 meV W. Pacuski et al, Phys. Rev. B 73 035214 (2006) Co2+ 2E 3d7 4F 5E 5D Mn3+ 3d4 5T2 S=3/2 S=2 Isoelectronic spins Magneto-optical spectroscopy of intraionic d-d transitions (Ga,Mn)N : 0.03% Mn Spin allowed transition at 1413 meV S. Marcet et al, cond-mat/0604025 2006 4A2

  22. Ground state : Fine structure Hamiltonian parameters Axial anisotropy : g//=1.91 gperp =1.98 Axial anisotropy : D=0.27 meV g//=2.28 Axial anisotropy : D=0.35 meV S. Marcet et al, cond-mat/0604025 2006

  23. Zn1-xCoxO Co2+ incorporation up to 6% W. Pacuski et al, Phys. Rev. B 73 035214 (2006) Evolution with of the magnetic ion concentration Ga1-xMnxN Mn3+ incoporation up to about 1%

  24. Zn1-xCoxO S. Marcet, Thèse Grenoble, 11/2005 No ferromagnetism observed up to 10% Ferromagnetism observed for PLD samples R. Galera, Lab. L. Néel, Grenoble Ferromagnetism observed for 6% Mn : Tc~5K Comparison with the magnetic properties Ga1-xMnxN 1.7% Mn 6%

  25. Energy CB s+ s- VB A B C ∆Eshift = 6meV xMn = 0.004 xMn = 0.004 N0|α-β|=0.8 eV <Sz> = 2 N0(α-β) =-1.2 eV ∆Eshift = 1 meV Exchange interactions with carriers x = 0.1% A B C

  26. Conclusion - II-VI Heterostructures : - Carrier induced in CdMnTe quantum wells : Modulation doping or surface doping • CdTe quantum dots doped with a single Mn ions : • Manipulation and detection of a single spins - High gap DMS : - High temperature ferromagnetism still controversial • GaMnN : Incorporation of isoelectronic Mn3+ ions : 3d4 • Ferromagnetic exchange with holes • Ferromagnetism observed at low temperature • ZnCoO : Incorporation of Co2+ isoelectronic ions • Paramagnetic behavior observed up to 10% Co • spin carrier exchange smaller than in GaMnN

  27. - Equipe mixte CEA-CNRS-UJF Grenoble, France L. Besombes, E. Bellet, Y. Biquard, J. Cibert, D. Halley, D. Ferrand, R. Giraud, S. Kuruda, E. Sarigianidou, H. Mariette Y. Leger, S. Marcet, L. Maingault, W. Pacuski, A. Titov - Lab. L. Néel, France, Grenoble R. Galera, M. Amara, B. Barbara, J. Cibert • Polish academy of science, IFPAN, Warsaw, Poland • M. Sawicki, J. Jaroszynsky, S. Kolesnik, T. Dietl - Université de Varsovie, Pologne W. Maslana, W. Pacuski, P. Kossacki, J Gaj E. Gheraeert, LEPES, Grenoble C. Deparis, C. Mohrain, CRHEA Valbonne K. Rode, M. Anane UMP CNRS-Thales, Orsay A. Dinia, E. Beaurepaire, M. Gallart, P. Gilliot IPCMS,Strasbourg, France - Institute of Materials Science, University of Tsukuba, Japan S. Marcet,. N. Nishizawa, T. Kumekawa, N. Ozaki, S. Kuroda and K. Takita

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