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

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) Kroutvar et al., Nature 432,81 (2004) Spin manipulation

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

Isoelectronic element II-VI semimagnetic heterostructures I II Valence mixte I, II, III… III IV V VI VII VIII H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Ru Rh Pd Ag Cd In Sn Sb Te Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn II Cd0.7Mg0.3Te Magnetic alloys : Cd1-xMnxTe, Zn1-xMnxTe Mn : 4s2 3d5 With a large Mn solubility up to 75% S=5/2 localized spins Isoelectronic element Almost perfect semiconducting properties L CdTe Cd0.7Mg0.3Te Cd0.88Zn0.12Te substrate CdTe/CdMgTe quantum wells ZnTe CdTe CdTe ZnTe ZnTe substrate CdTe/ZnTe quantum dots

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

p type modulation doped CdMnTe QWs Surface doped CdMnTe QW 15 nm < z < 60 nm After surface oxydation Mn Compositions 0-11% Hole densities 1-2 1011 cm-2 W. Maslana, 2003 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

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

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

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

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

Magnetic CdMnTe/ZnTe QDs Strained induced CdTe/ZnTe QDs: UHV-AFM image of CdTe QDs on ZnTe. "Stranski-Krastanow" h > hcSK 3D-coherent islands 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

CdTe/ZnTe QDs doped with a single Mn atom Single dot spectroscopy : Mn density = QDs density Strained induced Cd(Mn)Te/ZnTe QDs: Mn segregation during the growth of a spacer layer Thèse L Maingault, H. Mariette 100 mm Strained induced QDs To study in detail the magnetic interaction between a single ion and indivual carriers in a zero dimensional system we realized QDs with a low density of Mn magnetic ions. Take advantage of the intermixing of Mn during the growth…. Introduce individual spins in QDs: seggregation of Mn during the growth of a ZnTe spacer layer on a ZnMnTe layer Sparce distribution of Mn at the surface when you start the growth of the CdTe QD layer Target the same density of Mn and QDs Introduce Mn in QDs, but random distribution of spins and QDs. To access the optical properties of individual QDs … Thèse Y. Léger

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

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

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

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

II : High band gap diluted magnetic semiconductors GaMnN/ZnCoO 2. ZnCrTe I II Valence mixte I, II, III… III IV V VI VII VIII H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Ru Rh Pd Ag Cd In Sn Sb Te Xe Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn II-VI : Cr2+ : 4s2 3d4 Co2+ : 4s2 3d7 III-V Mn 4s2 3d5 Acceptor : GaMnAs 3d5 Isoelectronic : 3d4

Tc>300K Towards room temperature diluted magnetic semiconductors ? 2001 2002 (Ga,Mn)N 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

3d4 3d7 e t2 E E e t2 D.O.S Cr2+ in II-VI 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 e t2 BV BC E D.O.S Partially filled d bands located within the gap ? Cr2+ in II-VI Mn3+ in III-V 3d4 E BV BC e t2 Co2+ in ZnO 3d7 Ferromagnetism mediated by electrons ?

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

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

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

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

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

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

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

- 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