1. 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

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

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

5. Local Moments and Valence Band Splittings Simultaneously
Start from Scatch
Local Moments and Valence Band Splittings Simultaneously TM

6. 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: Cu
Ferromagnetism by clustering can be excluded

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

8. 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

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

10. Strength of p-d Hybridization
p-d hybridization results in a spin dependent coupling between the holes and the Mn ions.
TM in GaN
ΔEvalence (eV)
Noβ (eV)
Local Moment(μB) Fe
0.4203 4 Co
0.2902 3 Ni
0.3780 2 Cu
0.3961 1
GaAs:Mn
0.3231 5

11. Other Results Calculation Result Experimental Results
R. Wu et al. APL 89(2006)
Experimental Results
Ion Implantation
Nanowire
Appl. Phys. Lett. 90, (2007).
Adv. Mater., Submitted

12. 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)

13. Absolute Electronegativity
6.27
7.3
7.54
5.62
6.22
5.3
5.89

14. Why Cu is Good and Mn is Bad in GaN?
Cu doped GaN
Mn doped GaN 2p 3d σg
σu* TM N 3d 2p TM N Cu Mn
Electronegativity difference
Small
Large
d-character in antibonding state
Weaker
Stronger
Carrier in antibonding state
Delocalized
Localized

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