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First Principle Design of Diluted Magnetic Semiconductor: Cu doped GaN

First Principle Design of Diluted Magnetic Semiconductor: Cu doped GaN. S.-C. Lee * , K.-R. Lee, and K.-H. Lee Computational Science Center Korea Institute of Science and Technology, KOREA. Diluted Magnetic Semiconductors. Diluted Magnetic Semiconductor (DMS)

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First Principle Design of Diluted Magnetic Semiconductor: Cu doped GaN

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  1. First Principle Design of Diluted Magnetic Semiconductor: Cu doped GaN S.-C. Lee*, K.-R. Lee, and K.-H. Lee Computational Science Center Korea Institute of Science and Technology, KOREA

  2. Diluted Magnetic Semiconductors • Diluted Magnetic Semiconductor (DMS) • A ferromagnetic material that can be made by doping of impurities, especially transition metal elements, into a semiconductor host. • Conducting spin polarized carriers of DMS are used for spin injection. • Compatible with current semiconductor industry. Spin Field Effect Transistor

  3. TM TM TM Mechanisms of Ferromagnetism in DMS • Long-ranged interaction of transition metals via delocalized carrier can stabilize ferromagnetic phase. • All valence electrons of the anion atoms between TM should be spin polarized. • The spin polarized carrier can deliver information

  4. Success and Failure of Mn doped GaAs • Mn substitutes Ga in zincblende structure • Structure is compatible with GaAs 2DEG • Tc is correlated with carrier density • Ferromagnetic semiconductor with ordering temperature ~ 160 K • Finding a new DMS material having high Tc Mn Ku et al., APL 82 2302 (2003)

  5. Beyond GaMnAs T. Dietl, Semicond. Sci. Technol. 17 (2002) 377  What will happen if other transition elements are used as dopants?

  6. Mn doped GaN: Can it be a DMS? • Theoretically predicted by Dietl • High Tc was observed above room T. • Ferromagnetic behavior by SQUID experiments Positive Negative • Possibility of precipitates • XMCD or anomalous Hall Effect has not been observed. • Ferromagnetism can be achieved by short ranged double exchange mechanism Material specific or chemical effect has not been considered!

  7. TM TM Let’s Back to the DMS Basics Local Moments and Splitting Valence Bands Simultaneously

  8. Start from Scratch Design Rule: Finding a TM that induces spin polarization of valence band Transition Element (V, Cr, Mn, Fe, Co, Ni and Cu) 5th Nitrogen 1st NN Nitrogen 4th Nitrogen 3rd NN Nitrogen 2nd NN Nitrogen

  9. Calculation Methods • Planewave Pseudopotential Method: VASP.4.6.21 • XC functional: GGA(PW91) • Cutoff energy of Planewave: 800 eV • 4X4X4 k point mesh with MP • Electronic Relaxation: Davidson followed by RMM-DIIS • Structure Relaxation: Conjugate Gradient • Force Convergence Criterion: 0.01 eV/A • Gaussian Smearing with 0.1 eV for lm-DOS • Treatment of Ga 3d state • Semicore treatment for GaN • Core treatment for GaAs • TM dopant: V, Cr, Mn, Fe, Co, Ni, and Cu • Ferromagnetism by clustering can be excluded

  10. Electronic Structure of Mn doped GaAs Delocalized Carrier due to p-d Exchange Interaction Localized Moment due to Mn

  11. Magnetic Moments of TM in GaN Host Less-Than Half filled More-than Half filled

  12. Spin Density of TM doped GaN Less-Than Half filled GaN:Cr GaN:Mn More-than Half filled GaN:Co GaN:Cu

  13. Partial DOSs having More-than Half Filled States GaCoN: Half Metal GaFeN: Magnetic Insulator GaCuN: Half Metal GaNiN: Magnetic Insulator

  14. Valence Band Splitting SCL et al. JMMM (2007) SCL et al. Solid State Phenomena (2007)

  15. Strength of p-d Hybridization p-d hybridization results in a spin dependent coupling between the holes and the Mn ions.

  16. Magnetic Interaction in Larger Supercell 216-atom supercell

  17. Co, Cu Co, Cu Cu is the most probable candidate in GaN host

  18. Experimental Confirmation Nanowire Ion Implantation Appl. Phys. Lett. 90, 032504 (2007). NanoLett, Accepted 2007

  19. Stability of Ferromagnetic Cu Non-Magnetic Magnetic • Number of electrons in frontier level or unfilled states • Para: 0.98 for Cu, 3.2 for Total • Ferro: 0.27 for Cu, 0.82 for Total • Ferromagnetic alignment drastically decrease the number of electrons in frontier level “Antibonding conjecture” Dronskowski (2006)

  20. Electron Configurations of Non-Magnetic Phase t2g Mainly M d M-N Antibonding EF eg 4 antibonding d-character electrons in frontier level  Energetically unfavored M 3d sp3 Mainly p M-N Bonding

  21. Electron Configurations of Magnetic Phase t2g up down eg EF • Only 1 electron in frontier level • Energetically favored Spin polarized configuration can decrease the number of antibonding electrons M 3d sp3

  22. And More … Magnetic Non-Magnetic Spin-up Contracted Small Hybridization Short-ranged Spin-down Expanded Large Hybridization Long-ranged

  23. Magnetic Moments of TM in GaN Host Less-Than Half filled More-than Half filled

  24. Why Cu is good Mn is bad? Absolute Electronegativity 6.27 7.3 7.54 6.22 5.62 5.89 5.3

  25. σu* 3d 2p σg TM N Why Cu is Good and Mn is Bad in GaN? Cu doped GaN Mn doped GaN 3d 2p TM N

  26. Cu Cu Summary Electronegativity can help to design a novel DMS material Cu is a probable candidate. Quantitative analysis is also needed.

  27. Cu(in fcc metal)+Ga32N32 Ga(in orthorhombic)+ Ga31Cu1N32 Cu(in fcc metal)+Ga32N32 1/2N2(in N2 molecule)+Ga32N31Cu1 Cu(in fcc metal)+Ga32N32 Ga32N32Cu1 Formation Energies of Cu in GaN Host

  28. Cu Cu Local Moments of Cu • Total Magnetic Moment: 2.0 μB • Cu Projected Moment: 0.65 μB • Charge State: Cu+2 • Possible for Hole Doping: 3d9+h

  29. TM TM Roles of Transition Metal Impurities • Local Magnetic Moment • Split Valence Band Spin Polarized Carrier!!

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