Electronic and Magnetic Structure of Transition Metals doped GaN Seung-Cheol Lee, Kwang-Ryeol Lee, Kyu-Hwan Lee Future Technology Research Division, KIST, Korea

Spintronics and Spin FET D. Awschalom et al, Scientific American (2002) Spin Field Effect Transistor Semiconductor based device Conceptually, spin FET is similar to conventional FET. Charges of FET are controlled by induced bias voltage, while spins of electrons are controlled in spin FET. To do so, spin injection is the first step to realize spin FET. Find an effective material that can inject spin into the gate. Control of Spin and Charge of Electrons Simultaneously

Diluted Magnetic Semiconductors Diluted Magnetic Semoconductor (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 manipulation. - Compatible with current semiconductor industry. Spin Field Effect Transistor

Success and Failure of Ga 1-x Mn x As Mn substitutes Ga in zincblende structure –Structure is compatible with GaAs 2DEG T c is correlated with carrier density Ferromagnetic semiconductor with ordering temperature ~ 160 K Finding a new DMS material having high Tc Ku et al., APL (2003) Mn

Motivation: DMSs beyond Ga 1-x Mn x As T. Dietl, Semicond. Sci. Technol. 17 (2002) 377  What will happen if other transition elements are used as dopants?

Requirements for Successful DMS TM Local Moments and Splitting Valence Bands Simultaneously

Transition Element (V, Cr, Mn, Fe, Co, Ni and Cu) 1 st NN Nitrogen 4 th Nitrogen 2 nd NN Nitrogen 3 rd NN Nitrogen Which TM is Feasible in GaN Host? 5 th Nitrogen Design Rule: Finding a TM that induces spin polarization of valence band

 Planewave Pseudopotential Method: VASP  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 Methods

As stateTotal DOS and Mn d state*10 Example: Electronic Structure of GaMnAs Localized Moment due to Mn Delocalized Carrier due to p-d Exchange Interaction

More-than Half filled Total and Local Magnetic Moments Less-Than Half filled

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

More-than Half filled Total and Local Magnetic Moments Less-Than Half filled

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

Up SpinDown SpinUp Spin t 2g egeg Filled ElectronUnfilled Electron Up SpinDown SpinUp Spin GaN:Mn(7)-half metal GaN:Co(9)-half metal Up SpinDown SpinUp Spin GaN:Ni(10)-insulator Up SpinDown SpinUp Spin GaN:Cu(11)-half metal Electron Occupation in GaN No Splitting of Valence p-band

Hamiltonian based on p-d Hybridization p-d hybridization results in a spin dependent coupling between the holes and the Mn ions. TM in GaNΔE valence (eV)N o β (eV) Local Moment(μ B ) Fe Co Ni Cu GaAs:Mn

Summary Co, Cu