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ICMAT2007-SCLee

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									Search for a New Diluted Magnetic
Semiconductor using First Principle
    Calculations: Cu doped GaN


     S.-C. Lee*, K.-R. Lee, and K.-H. Lee

           Computational Science Center
 Korea Institute of Science and Technology, KOREA


                               6 July 2007, Suntec Convention Center
Diluted Magnetic Semiconductors
ü 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
Roles of Transition Metal Impurities

ü Local Magnetic Moment    ü Split Valence Band




TM           TM
                              Spin Polarized Carrier!!
Beyond GaMnAs




                                T. Dietl, Semicond. Sci. Technol. 17 (2002) 377

è What will happen if other transition elements are used as dopants?
Start from Scatch

     Local Moments and Valence Band Splittings Simultaneously




                    TM
                                             TM
Calculation Methods

u   Planewave Pseudopotential Method: VASP.4.6.21
u   XC functional: GGA(PW91)
u   Cutoff energy of Planewave: 800 eV
u   4X4X4 k point mesh with MP
u   Electronic Relaxation: Davidson followed by RMM-DIIS
u   Structure Relaxation: Conjugate Gradient
u   Force Convergence Criterion: 0.01 eV/A
u   Gaussian Smearing with 0.1 eV for lm-DOS
u   Treatment of Ga 3d state
    u Semicore treatment for GaN
    u Core treatment for GaAs
u TM dopant: Cu
    u Ferromagnetism by clustering can be excluded
Formation Energies of Cu in GaN Host




                                  Formation Energy of Cu
                                   CuGa            0.00
                                    CuN            2.56
                                    CuI            5.42




  Cu(in fcc metal)+Ga32N32 à Ga(in orthorhombic)+
  Ga31Cu1N32
  Cu(in fcc metal)+Ga32N32 à 1/2N2(in N2 molecule)+Ga32N31Cu1
  Cu(in fcc metal)+Ga32N32 à Ga32N32Cu1
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




Cu          Cu
Valence Band Splitting




                         SCL et al. JMMM (2007)
                         SCL et al. Solid State Phenomena (2007)
 Strength of p-d Hybridization

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




                                                      Local
  TM in GaN      ΔEvalence (eV)      N o β(eV)
                                                    Moment( μ)
                                                             B

      Fe            0.4203           -3.3624            4
      Co            0.2902           -3.0955            3
      Ni            0.3780           -6.0480            2
      Cu            0.3961          -12.6752            1
   GaAs:Mn          0.3231           -2.0678            5
Other Results
• Calculation Result
   – R. Wu et al. APL 89(2006) 062505
• Experimental Results
       Ion Implantation                      Nanowire




 Appl. Phys. Lett. 90, 032504 (2007).   Adv. Mater., Submitted
 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
èFerromagnetic alignment drastically decrease the number of electrons in frontier level



                                                  “Antibonding conjecture” Dronskowski (2006)
Absolute Electronegativity


                             6.27   7.3    7.54


                                    5.62   6.22


                                    5.3    5.89
Why Cu is Good and Mn is Bad in GaN?
          Cu doped GaN                                   Mn doped GaN


                         σu*




                                             3d
3d
                                      2p                                     2p
       TM                σg                         TM
                               N                                        N



                                               Cu                   Mn
       Electronegativity difference          Small                Large
     d-character in antibonding state       Weaker               Stronger
       Carrier in antibonding state        Delocalized           Localized
Summary


  Cu is a probable candidate.   Electronegativity can help to
                                design a novel DMS material




      Cu            Cu




                                Quantitative analysis is also
                                needed

								
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