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 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 Local Magnetic Moment Split Valence Band TM TM Spin Polarized Carrier!!

 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?

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

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

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

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. TM in GaN ΔEvalence (eV) Noβ (eV) Local Moment(μB) 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 Experimental Results 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 Ferromagnetic 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 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

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