전이금속이 포함된 GaN 의 전자구조 및 자기적 특성해석

이승철 , 이광렬한국과학기술연구원 미래기술연구본부

30 회 학술대회 , 광운대학교

SpintronicsSpintronics

D. Awschalom et al, Scientific American (2002)

Magnetic Tunneling Junction Spin Field Effect Transistor

• Spin dependent tunneling• Magnetic RAM

• Semiconductor based device• Next generation of spintronics

Control of Spin and Charge of Electrons Simultaneously

Models for Ferromagnetism DMSModels for Ferromagnetism DMS

• Multiple impurities trapped by few carriers

(percolation of magnetic polarons)

• Impurity induces a polarization in the host

(RKKY type interaction)

Localized magnetic moment surrounded by non-local carrier

TM

Induced hole

Success and Failure of Ga1-xMnxAsSuccess 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

Ku et al., APL 82 2302 (2003)

Mn

As stateTotal DOS and Mn d state*10

GaMnAsGaMnAs

DMSs beyond Ga1-xMnxAsDMSs beyond Ga1-xMnxAs

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

Requirements for DMS MaterialsRequirements for DMS Materials

1. The carriers (holes) are polarized and DMS can serve as efficient sources for spin injection.

2. Because Curie temperature is correlated with the carrier concentration, the magnetic order can be manipulated with voltage.

Models for Ferromagnetism in Ga1-

xMnxAsModels for Ferromagnetism in Ga1-

xMnxAs

• Multiple impurities trapped by few carriers(percolation of magnetic polarons)

• Impurity induces a polarization in the host(RKKY type interaction)

Localized magnetic moment surrounded by non-local carrier

TM

Induced hole

Research Results Related to GaN:TMResearch Results Related to GaN:TM

1. GaN:Mn• Most of the studies based on GaN host has focused o

n this system.• Short range interaction of Mn.• Self interaction of electrons might be important in this

system.

2. GaN:Cr• This system is based on the prediction of Sato et al.

3. Almost all the studies have focused on the magnetic interaction between transition metal ion.

First Principle CalculationFirst Principle Calculation• Density Functional Theory• Kohn-Sham Eq. ( Single Electron Schrodinger Equation)

KS KS KSeffH E

• Results Obtained from the Kohn-Sham Equation– Cohesive energy– Charge density– Electronic structure (band, DOS)– Nature of bonding– STM image simulation– Etc

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

Calculation ConditionCalculation Condition

Transition Metal

1st NN Nitrogen 4th Nitrogen

2nd NN Nitrogen 3rd NN Nitrogen

Structure of 64-Atom GaNStructure of 64-Atom GaN

5th Nitrogen

3d Transition Metals3d Transition Metals

Mn doped GaAs and GaNMn doped GaAs and GaN

GaMnNGaMnAs

GaCrNGaVN

Partial DOSs having less-than half filled d state

GaMnN

Up Spin Down SpinUp SpinUp Spin

t2g

eg

GaN:Mn(7)

GaFeN

GaCoN

GaNiN GaCuN

Partial DOSs having more-than half filled d state

Up Spin Down SpinUp SpinUp Spin

t2g

eg

Filled Electron Unfilled Electron

Up Spin Down SpinUp SpinUp Spin

GaN:Mn(7) GaN:Co(9)

Up Spin Down SpinUp SpinUp Spin

GaN:Ni(10)

Up Spin Down SpinUp SpinUp Spin

GaN:Cu(11)

Electron Occupation in GaNElectron Occupation in GaNNo

Splitting of Valence p-

band

Magnetic Moments of Nitrogen

1st N 2nd N 3rd N 4th N-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

Ma

gn

etic

Mo

me

nt (

/ato

m)

Cu Ni Co Fe Mn Cr V GaAs:Mn

Total and TM Local Magnetic Moments

Half filled d electrons of TM

3+ valency 2+ valency

V, Cr, Mn

Fe, Co, Ni, Cu

Interaction Range of TM

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.