전이금속이 포함된 GaN 의 전자구조 및 자기적 특성해석

1. 30회 학술대회, 광운대학교 전이금속이 포함된 GaN의 전자구조 및 자기적 특성해석 이승철, 이광렬 한국과학기술연구원 미래기술연구본부

2. Spintronics Control of Spin and Charge of Electrons Simultaneously Magnetic Tunneling Junction Spin Field Effect Transistor • Spin dependent tunneling • Magnetic RAM • Semiconductor based device • Next generation of spintronics D. Awschalom et al, Scientific American (2002)

3. Models for Ferromagnetism DMS Localized magnetic moment surrounded by non-local carrier • Impurity induces a polarization in the host (RKKY type interaction) TM Induced hole • Multiple impurities trapped by few carriers (percolation of magnetic polarons)

4. Success and Failure of Ga1-xMnxAs • 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 Mn Ku et al., APL 82 2302 (2003)

5. GaMnAs Total DOS and Mn d state*10 As state

6. DMSs beyond Ga1-xMnxAs T. Dietl, Semicond. Sci. Technol. 17 (2002) 377

7. Requirements for DMS Materials • The carriers (holes) are polarized and DMS can serve as efficient sources for spin injection. • Because Curie temperature is correlated with the carrier concentration, the magnetic order can be manipulated with voltage.

8. Models for Ferromagnetism in Ga1-xMnxAs Localized magnetic moment surrounded by non-local carrier • Impurity induces a polarization in the host (RKKY type interaction) TM Induced hole • Multiple impurities trapped by few carriers (percolation of magnetic polarons)

9. Research Results Related to GaN:TM • GaN:Mn • Most of the studies based on GaN host has focused on this system. • Short range interaction of Mn. • Self interaction of electrons might be important in this system. • GaN:Cr • This system is based on the prediction of Sato et al. • Almost all the studies have focused on the magnetic interaction between transition metal ion.

10. First Principle Calculation • Density Functional Theory • Kohn-Sham Eq. ( Single Electron Schrodinger Equation) • Results Obtained from the Kohn-Sham Equation • Cohesive energy • Charge density • Electronic structure (band, DOS) • Nature of bonding • STM image simulation • Etc

11. Calculation Condition • 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

12. Structure of 64-Atom GaN Transition Metal 5th Nitrogen 1st NN Nitrogen 4th Nitrogen 3rd NN Nitrogen 2nd NN Nitrogen

13. 3d Transition Metals

14. Mn doped GaAs and GaN GaMnN GaMnAs

15. Partial DOSs having less-than half filled d state GaVN GaCrN GaMnN GaN:Mn(7) Up Spin Up Spin Up Spin Down Spin t2g eg

16. Partial DOSs having more-than half filled d state GaCoN GaFeN GaCuN GaNiN

17. Electron Occupation in GaN No Splitting of Valence p-band GaN:Co(9) GaN:Mn(7) Up Spin Up Spin Up Spin Down Spin Up Spin Up Spin Up Spin Down Spin t2g eg GaN:Ni(10) GaN:Cu(11) Up Spin Up Spin Up Spin Down Spin Up Spin Up Spin Up Spin Down Spin Filled Electron Unfilled Electron

18. Magnetic Moments of Nitrogen

19. Total and TM Local Magnetic Moments Half filled d electrons of TM 3+ valency 2+ valency

20. Interaction Range of TM V, Cr, Mn Fe, Co, Ni, Cu

21. Summary • Electronic and magnetic properties of transition metal doped GaN was studied using first principle calculation. • Valence band splitting was observed in the cases of Fe, Co, Ni, and Cu, which have more-than-half-filled character. • Cu doped GaN was predicted as the most probable candidates for DMS material. • Further studies on magnetic interaction should be followed to confirm the prediction.