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전이금속의 도핑에 따른 질화물계의 전자구조 및 자기적 특성 변화

전이금속의 도핑에 따른 질화물계의 전자구조 및 자기적 특성 변화. S.C. Lee 1 , K.R. Lee 1 , K.H. Lee 1 , W. Temmerman 2 1 Future Technology Research Division, KIST, Korea 2 Band Theory Group, Daresbury Laboratory, UK. Spintronics Devices. Control of Spin and Charge of Electrons Simultaneously.

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전이금속의 도핑에 따른 질화물계의 전자구조 및 자기적 특성 변화

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  1. 전이금속의 도핑에 따른 질화물계의 전자구조 및 자기적 특성 변화 S.C. Lee1, K.R. Lee1, K.H. Lee1, W. Temmerman2 1 Future Technology Research Division, KIST, Korea 2 Band Theory Group, Daresbury Laboratory, UK

  2. Spintronics Devices Control of Spin and Charge of Electrons Simultaneously Magnetic Tunneling Junction Spin Field Effect Transistor • Magnetic RAM • GMR: HDD Read Head • Semiconductor based device • Next Generation of Spintronics D. Awschalom et al, Sci.Am.(2002)

  3. Spin Injection from FM Metal to SC FM Metal PM SC Spin Injection G. Schmidt et al., Phys. Rev. B 62, 4790 (2000)

  4. Possible Solutions • Diluted magnetic semiconductors (DMS): σsc/σfm ~ 1 • Fielderling et al., Nature 402 787 (1999) • Ohno et al. Nature 402 790 (1999) • Half metallic ferromagnets: β ~ 1 • Tunneling barrier at the FM/SC interaction • Rashiba, Phys. Rev. B 62, 16267 (2000) • Intrinsic Schottky barrier • Zhu et al., Phys. Rev. Lett. 87, 016601 (2001) • Hanbicki et al. Appl. Phys. Lett. 80, 1240 (2002) • Spin-dependent interface resistance • Fert and Jaffres, Phys. Rev. B 64, 184420 (2001) • Zwierzycki et al. arXiv:cond-mat/0204422 (2002)

  5. Conditions for Successful DMS • DMS should show ferromagnetism. • Origin of FM should be the diluted transition metal. • Clustering or third phase formation should be avoided. • Curie temperature should be higher than room temperature. • Ferromagnetic behavior should operate at room temperature. • Carrier of semiconductor should be spin polarized. • Spin polarized carrier is essential for application. • Selected material should be compatible to the semiconductor process.

  6. Magnetic Properties of Ga1-xMnxAs • Mn can substitute Ga in GaAs of zinc blende structure. • Tc is correlated with carrier density. • Ferromagnetic semiconductor with ordering temperature ~ 160K Max. Matsukura et. al. PRB (1998)

  7. TM Induced hole Impurity induced polarization in the host (RKKY type) Magnetic Properties of Ga1-xMnxAs Ku et al., Appl. Phys. Lett. 82, 2302 (2003).

  8. DMSs of High Tc T. Dietl, Semicond. Sci. Technol. 17 (2002) 377

  9. General Overview of GaN • Wide band gap semiconductor: • Direct band gap with Eg=3.5 eV (W), 3.29~3.35 (ZB) • Generally wurtzite, but zinc blend structure is also possible. • Intrinsic n-type semiconductor • Mg has known to be the only one element for p-type doping. • Applications • Short-wavelength LED • High power/high temperature electronics Possibility of High Tc DMS when doped with Mn.

  10. Calculation Method • 64 atoms (2x2x2 supercell) • VASP (Vienna Ab-initio Simulation Package) • Planewave pseudopotential • GGA(PW91) exchange-correlation potential • Ecut: 400 eV • Fully relaxed atomic structure • 4x4x4 Monkhorst-Pack k-point mesh • Wurzite and zinc blende GaN structures

  11. Down Spin Up Spin t2g eg Ga0.97Mn0.03N Wurtzite • Fermi level locates at the unpaired and localized Mn t2g orbital with large ΔCR (1.5 eV) • Possibly high magnetic moment (4mB) • Large Exchange Splitting: ΔCR (1.5 eV) < ΔEX (2.1 eV) ΔCR ΔEX GaN:Mn(7-3)

  12. 3d Orbital Configuration

  13. Orbital Degeneracy wrt Crystal Structure Tetrahedral Configuration Octahedral Configuration eg t2g Crystal Field Splitting Crystal Field Splitting,ΔCR eg t2g

  14. Down Spin Up Spin t2g eg Ga0.97Mn0.03N Wurtzite • Fermi level locates at the unpaired and localized Mn t2g orbital with large ΔCR (1.5 eV) • Possibly high magnetic moment (4mB) • Large Exchange Splitting: ΔCR (1.5 eV) < ΔEX (2.1 eV) • No valence band splitting : no carrier polarization : Major problem ΔCR ΔEX GaN:Mn(7-3)

  15. ΔCR ΔEX Ga0.97Mn0.03N Zinc Blende Wurtzite

  16. Comparison of GaMnAs and GaMnN GaMnAs GaMnN • Mn in GaAs polarize the host valence band edge, which results in the formation of spin polarized carrier (hole) in host GaAs.

  17. Up Spin Down Spin t2g eg Ga0.97Ni0.03N Wurtzite GaN:Ni(10-3) • Ni doped GaN exhibits an insulating behavior. • Spin down eg state is fully occupied by electrons. • Relatively larger exchange splitting behavior.

  18. Down Spin Up Spin t2g eg Ga0.97Cu0.03N Wurtzite GaN:Cu(11-3) • Fermi level locates at the unpaired spin down Cu t2g orbital. • Degree of localization is much smaller than that of GaN:Mn. • Exchange splitting is smaller. • Stronger hybridization between Cu 3d – N 2p state

  19. Summary GaMnN GaCuN

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