Quantum-functional Semiconductor Research Center, Dongguk University Nammee Kim QSRC, Dongguk University
Dec 30, 2015
Quantum-functional Semiconductor Research Center, Dongguk University
Nammee Kim
QSRC, Dongguk University
Quantum-functional Semiconductor Research Center, Dongguk University
Current Research Topics
• Magnetic Quantum Structures (Dot, Ring)
• Diluted Magnetic Semiconductors (DMS)
• Ferro-Electric Semiconductors (FES)
Quantum-functional Semiconductor Research Center, Dongguk University
Contents
1. Motivation 2. Review on DMS 3. My Research on DMS
4. Future Research Plan
5. Conclusion
Quantum-functional Semiconductor Research Center, Dongguk University
1. Motivation
size: the wedge is 1.25 inches to a side.
1947-point contact transistor
1956-Nobel Prize
(Brattain, Bardeen, Shockley)
Central Processing Unit (CPU)
Quantum-functional Semiconductor Research Center, Dongguk University
Year of introduction Transistors
4004 1971 2,250
8008 1972 2,500
8080 1974 5,000
8086 1978 29,000
286 1982 120,000
386™ processor 1985 275,000
486™ DX processor 1989 1,180,000
Pentium® processor 1993 3,100,000
Pentium II processor 1997 7,500,000
Pentium III processor 1999 24,000,000
Pentium 4 processor 2000 42,000,000
Moore’s law: With price kept constant, the processing power of microchips doubles every 18 months.(1965)
Quantum-functional Semiconductor Research Center, Dongguk University
Limitation of Conventional Semiconductor Device
Semiconductor Device
Limitation of size reduction( energy quantization, quantum interference etc.)
What physics?
What materials?
What device structures?
Quantum-functional Semiconductor Research Center, Dongguk University
Spintronics? Spintronics involves the study of active control and manipulation of spin degree of freedom in solid-state system.
• Electronics – charge metal, doped semiconductors
• Spintronics – charge+ spin metal, doped semiconductors, magnetic materials
Quantum-functional Semiconductor Research Center, Dongguk University
• Capable of much higher speed at very low
power, higher density, and nonvolatile
• Spin FET, spin LED, Spin RTD, etc.
Conventional semiconductor
s
Spin-Electronics
Ferromagnetic materials
spin echarge
e
Hybrid
This technology exists between the magnetism and electronics of semiconductors.
Quantum-functional Semiconductor Research Center, Dongguk University
Conventional non-magnetic semiconductors (II-VI, III-V..)
PLUS Magnetic Elements (Mn, Co, Ni, Fe…)
History• II-VI DMS
CdMnSe, ZnMnTe, HgMnTe...
J. K. Furdyna, J. Appl. Phys. 64, R29 (1988)
• III-V DMS
InMnAs, GaMnAs, GaMnN, ZnMnO…
H. Munekata et al., PRL 63, 1849 (1989)
H. Ohno et al., J. Magn. Magn. Mater. 200, 110 (1999).
2. Diluted Magnetic Semiconductors (DMS)
Quantum-functional Semiconductor Research Center, Dongguk University
Main Issues in DMS
Enhance Tc (Curie Temp.) above Room temperature
Structures and Materials
Control of ferromagnetism
Quantum-functional Semiconductor Research Center, Dongguk University
Research progresses
Enhance Tc of GaMnAs
H. Ohno et al., J. Magn. Magn. Mater. 200, 110(1999)
Tc = 110 K with x=0.05
1. Optimal Doping Rate in As grown sample
2. Effect of annealing
Ku et al., APL 82, 2302 (2003)
Tc = 160 K with x=0.085
Quantum-functional Semiconductor Research Center, Dongguk University
3. Effect of selective doping and annealing
M. Tanaka et al . APL 80, 3120 (2002) Tc=170 KCond-matt:0503444 – 192 K (I-HEMT), 250 K (N-MEMP)
Quantum-functional Semiconductor Research Center, Dongguk University
4. Structural Method (Digital alloy)
Result of TEM GaSb (12 ML)/Mn (0.5ML)
-1500 -1000 -500 0 500 1000 1500
-4
-2
0
2
4
6
Magnetic Field (Gauss)
M (
10-5
em
u)
5 K100K
285 K
layer containing Mn
H. Luo et al., Appl. Phys. Lett. 81, 511 (2002)
Quantum-functional Semiconductor Research Center, Dongguk University
T. Dietl, SCIENCE 287, 1019 (2000)
Quantum-functional Semiconductor Research Center, Dongguk University
Electric-field Control of Ferromagnetism
H. Ohno, Nature 408, 944 (2000)
Quantum-functional Semiconductor Research Center, Dongguk University
1. Controllable spin polarization of carriers in a DMS quantum dot (ssc submitted)
2. Ferromagnetic properties of Mn-doped III-V semiconductor quantum wells (Superconductivity/Novel Magnetism, 18, 189-193 (2005))
3. Magnetic properties of p-doped GaMnN diluted magnetic semiconductor containing clusters (Solid State Commun. 133, 629-633 (2005))
4. Numerical study of ferromagnetism of a GaMnN quantum well (J. Korean Phys. Soc. 45, 568-571 (2004))
5. Curie Temperatures of Magnetically Heavily Doped III-V/Mn Alloys(J. Korean Phys. Soc. 45, 647-649 (2004))
6. Effect of cluster-type on the Ferromagnetism of a GaMnN quantum well (Phys. Lett. A , 329, 226-230 (2004))
3. My Research on DMS
Quantum-functional Semiconductor Research Center, Dongguk University
7. Curie temperature modulation by electric fields in Mn delta-doped asymmetric double quantum well (Phys. Rev. B 69, 115308.1-115308.4 (2004))
8. Model study on the magnetization of digital alloys (Phys. Rev. B 68, 172406.1-172406.4 (2003))
9. Growth of ferromagnetic semiconducting Si:Mn film by Vacuum Evaporation Method (Chem. Mater.15, 3964 (2003))
10. Study on phase transitions of III-Mn-V diluted magnetic semiconductor quantum wires (Phys. Lett. A 302, 341-344 (2002))
11. Finite-Temperature Study of a Modulation-Doped DMS Quantum Well with Broken Spin Symmetry (Physica E 12, 383-387(2002))
12. Magnetization of a diluted magnetic semiconductor quantum well in a parallel magnetic field (J. Korean Phys. Soc. 39 , 1050-1054 (2001)
Quantum-functional Semiconductor Research Center, Dongguk University
Previous theoretical studies on III-V DMS quantum wells have predicted ….
B. Lee, T.Jungwirth, A.H.MacDonald PRB 61, 15606 (2000)
4
0
)0(2
*20 )(
12
1
w
nt
Bc zdz
m
k
SSxNT
d/1~
L.Bery and F. Guinea PRL 85 ,2384 (2000)
3/2
2
3/12
0
2
*
2
20
331
1
12
1
dt
Bc
nw
em
SSxN
kT
Purpose of this work:To know the dependence of Tc on free carrier density, magnetic impurity density and spin-exchange interaction energy!!!To compare the magnetic properties of In1-xMnxP and Ga1-
xMnxN.
1. Ferromagnetic properties of Mn-doped III-V semiconductor quantum wells (J. Superconductivity/Novel Magnetism, 18, 189-193 (2005))
Quantum-functional Semiconductor Research Center, Dongguk University
xcHpdconfEK VVVVHH ..
Hamiltonian
Quantum-functional Semiconductor Research Center, Dongguk University
zpzpzpz D2/ * Spin- polarization:
zpzpzp D 2
* Hole-density:
Quantum-functional Semiconductor Research Center, Dongguk University
)(, znn
zpzp ,
Pat T vs. 2D P vs. 2DcT
Self-Consistent CalculationSelf-Consistent Calculation
Quantum-functional Semiconductor Research Center, Dongguk University
Case of In1-xMnxP quantum well Case of In1-xMnxP quantum well
The dependence of the Tc on the carrier density of In1-xMnxP exhibits step-like behavior due to the discrete energy subbands by confinement effects.The Tc of the p-type In1-xMnxP quantum wells increases as the magnetic impurity density and the spin-exchange interaction energy increase.
Quantum-functional Semiconductor Research Center, Dongguk University
Case of Ga1-xMnxN quantum well Case of Ga1-xMnxN quantum well
Ga1-xMnxN shows weak step-like behavior compared to other III-Mn-V DMS quantum wells because the hole effective mass of Ga1-xMnxN is very large and the large hole effective mass reduces the energy splitting due to the confinement effects.
Contributions: Verify the relation between Tc and the carrier density quantitatively. Surely Ga1-xMnxN has Tc above room temperature as predicted by Dietl.
Quantum-functional Semiconductor Research Center, Dongguk University
V
B
hz
1 2 3 4 5
1D 1W 2W 2D
hV
Kim-fig1
gF
T. Dietl et al. PRB 55, R3347(1997)
A.H.MacDonald et al. PRB 61,15606(2000)
2. Curie temperature modulation by electric fields in Mn delta-doped asymmetric double quantum well (Phys. Rev. B 69, 115308.1-115308.4 (2004))
Purpose of this work: to suggest a quantum structure to enhance Tc and to control ferromagnetism by the external electric field.
M. Tanaka et al . APL 80, 3120 (2002)
Quantum-functional Semiconductor Research Center, Dongguk University
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.00.0
0.5
1.0
1.5
2.0
-15.0 -12.5 -10.0 -7.5 -5.0 -2.5 0.00.000
0.004
0.008
0.012
0.016
0.020
Fg(meV/nm)
W1=10nm, W
2=0nm
center-doped edge-doped
Tc/T
c01
Zh(nm)
Fg=0.0 meV/nm
Fg=5.1 meV/nm
Fg=7.0 meV/nm
Kim-fig2
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.00
1
2
3
4
5
6
7
8
9
10
-20 -15 -10 -5 0 5 10 15 200.000
0.004
0.008
0.012
0.016
0.020
Fg(meV/nm)
w1=10nm, w
2=10nm, B=5nm
center-doped edge-doped
Tc/T
c02
zh(nm)
Fg = 0.1 meV/nm
Fg = 0.5 meV/nm
Fg = 3.0 meV/nm
Kim-fig3
The Curie temperature is enhanced up to eight times higher than the case of no external electric fields for both of the Mn edge-doped and Mn center-doped samples.
The change of the Tc as a function of the applied electric fieldsThe change of the fourth power of the growth direction envelope function of carriers at the lowest subband.
Quantum-functional Semiconductor Research Center, Dongguk University
Effect of the well width
5 6 7 8 9 10 11 12 13 14 150
1
2
3
4
5
6
7
8
9
10
Tc/ T
c02
W2(nm)
W1=10nm, B=5nm, F
g=0.5meV/nm
center-doped edge-doped
Kim-fig4
The Curie temperature is controlled not only by applied electric fields but also by asymmetry (or amount of p-dopants) of wells.
Contributions: Propose a quantum structure to enhance Tc of DMS by applying an electric field to a Mn-delta-doped asymmetric double quantum well structure.
Quantum-functional Semiconductor Research Center, Dongguk University
Isolated Mn ions
Quasi-2D Islands
Model
3. Model study on the magnetization of digital alloys (Phys. Rev. B 68, 172406.1-172406.4 (2003))
layer containing Mn
Purpose of this work: To propose a new model of 2D system applied to the individual Mn layer in digital alloys to explain ferromagnetism of digital alloys.
H. Luo et al., Appl. Phys. Lett. 81, 511 (2002)
Quantum-functional Semiconductor Research Center, Dongguk University
0 50 100 150 200 250 300 350 400
1
2
3
4
5
6
M (
10
-7 e
mu
)
T(K)
The magnetization of digital alloys also strongly depends on the carrier and Mn ion concentrations and distribution of Mn ions in the system.
Quantum-functional Semiconductor Research Center, Dongguk University
-1500 -1000 -500 0 500 1000 1500
-4
-2
0
2
4
6
Magnetic Field (Gauss)
M (
10
-5 e
mu
)
5 K100K
285 K
This model produces temperature dependent magnetization as a function of external magnetic field qualitatively.
Contributions: Propose a new model for the digital alloys to explain the ferromagnetic mechanism and magnetic properties of the digital alloys successfully
Appl. Phys. Lett. 81, 511 (2002)
Quantum-functional Semiconductor Research Center, Dongguk University
4. Future Research Plan
Purpose: to achieve new concept quantum structures and Devices.
1. SPFET (Spin Polarized Field Effect Transistor)- spin polarization, spin injection, spin transport
2. Multi-ferroic material and quantum structures- combine DMS and FES
Quantum-functional Semiconductor Research Center, Dongguk University
1. Spin polarized field effect transistor
Suggested by S. Datta and B. Das,
Appl. Phys. Lett. 56, 665(1990)
2
2
22
2
22
/2)(
/2
2/)(
2/)(
ˆ
21
21
2
11
LmLkk
mkk
kmkE
kmkE
zkH
xx
xx
xx
xx
R
• Rashba Hamiltonian(LS coupling)
Quantum-functional Semiconductor Research Center, Dongguk University
Schematic idea of the spin transistor
With a gate voltage V1, spin of electrons precess with π between two ferromagnets.
Expect high resistance
With a gate voltage V2, spin of electrons precess with 2π between two ferromagnets.
Expect low resistance
Quantum-functional Semiconductor Research Center, Dongguk University
Requirements for a spin transistor
1. spin polarizer & spin detector (collector) cf> Ferromagnetic material such as permalloy (Ni80Fe20) or iron polarize about 45% of electron spins
2. High spin injection rate - low resistivity mismatch
3. 2 dimensional electron gas(2DEG) channel- 1dimensional channel high mobility high carrier concentration large spin-orbit interaction parameter
cf>Surface states of semiconductor, 2DES----InAs, GaAs…… spin life time > 100 ns, coherent travel distance > 100 micro m
4. control of spin precession coherent propagation of spin
Quantum-functional Semiconductor Research Center, Dongguk University
G
S.I. GaAs(100)
Metal MetalInMnAs Q.D.
InAs wetting layer
GaAs (channel)AlGaAs
DMS DMS
Quantum-functional Semiconductor Research Center, Dongguk University
Example 1: Mutiferroic BaTiO3-CoFe2O4 nanostructures H. Zheng et al., Science 303,661 (2004).
CoFe2O4-spinel BaTiO3-perovskiteSrTiO3 (001) SubstrateBy Pulsed laser deposition
2. Multi-ferroic materials
Quantum-functional Semiconductor Research Center, Dongguk University
Example 2: Epitaxial BiFeO3 multiferroic thin film heterostructures, J. Wang et al.,Science 299, 1719 (2003).
Quantum-functional Semiconductor Research Center, Dongguk University
Diluted Magnetic Semiconductors (DMS)Ferromagnetic
Multilayer Structures
Ferro-Electric Semiconductors(FES)Ferroelectric
ZnCrTe ZnLiMnO
ZnCdTe ZnLiO
ZnCrTe ZnLiMnOFM
FM CMS:Au
CMS:Au
CMSFES
ZnCrTe
ZnCrTe
CdZnS
Quantum-functional Semiconductor Research Center, Dongguk University
FES FES
Gate(Au)
ID
VD-S
Parallel polarization
Anti-parallel polarization
(VG = constant)
Si
Dipole Valve
DMS
FES
Insulator
QuaternaryQuaternaryFESFES 의 의 dipole dipole DMSDMS 의 의 spinspin
Quaternary
Quantum-functional Semiconductor Research Center, Dongguk University
Spintronics will find a breakthrough to overcome the limitation of semiconductor devices.
DMS is a good candidate of spintronics materials.
We have accomplished good contributions to the developments of DMS materials and structures experimentally as well as theoretically.
Future plans developing spintronics devices based on these study will open the new concept quantum computers and artificial intelligence, which are expected to change the paradigm of the future information society.
5. Conclusion
Thank you for your attention!!!!!