Study on the Diluted Magnetic Semiconductors

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Study on the Diluted Magnetic Semiconductors
Nammee Kim QSRC, Dongguk University
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• Current Research Topics
• Magnetic Quantum Structures (Dot, Ring)
• Diluted Magnetic Semiconductors (DMS)
• Ferro-Electric Semiconductors (FES)

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Contents 1. Motivation 2. Review on
DMS 3. My Research on
DMS 4. Future Research Plan 5. Conclusion
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1. Motivation
1947-point contact transistor 1956-Nobel
Prize (Brattain, Bardeen, Shockley)
size the wedge is 1.25 inches to a side.
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Moores law With price kept constant, the
processing power of microchips doubles every 18
months.(1965)
  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
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Semiconductor Device
Limitation of size reduction ( energy
quantization, quantum interference etc.)
Limitation of Conventional Semiconductor Device
What physics?
What materials?
What device structures?
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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

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This technology exists between the magnetism and
electronics of semiconductors.
Conventional semiconductors
Ferromagnetic materials
Hybrid
charge
spin
Spin-Electronics

• Capable of much higher speed at very low
• power, higher density, and nonvolatile
• Spin FET, spin LED, Spin RTD, etc.

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2. Diluted Magnetic Semiconductors (DMS)

• 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).

Conventional non-magnetic semiconductors (II-VI,
III-V..) PLUS Magnetic Elements (Mn, Co, Ni, Fe)
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Main Issues in DMS

• Enhance Tc (Curie Temp.) above Room
  temperature
• Structures and Materials
• Control of ferromagnetism

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• Research progresses
• Enhance Tc of GaMnAs

2. Effect of annealing
1. Optimal Doping Rate in As grown sample
H. Ohno et al., J. Magn. Magn. Mater. 200,
110(1999) Tc 110 K with x0.05
Ku et al., APL 82, 2302 (2003) Tc 160 K with
x0.085
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3. Effect of selective doping and annealing
M. Tanaka et al . APL 80, 3120 (2002) Tc170
K Cond-matt0503444 192 K (I-HEMT), 250 K
(N-MEMP)
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4. Structural Method (Digital alloy) Result of
TEM GaSb (12 ML)/Mn (0.5ML)
layer containing Mn
H. Luo et al., Appl. Phys. Lett. 81, 511 (2002)
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T. Dietl, SCIENCE 287, 1019 (2000)
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• Electric-field Control of Ferromagnetism

H. Ohno, Nature 408, 944 (2000)
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3. My Research on DMS
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/No
vel 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))
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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 SiMn 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)
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1. Ferromagnetic properties of Mn-doped III-V
semiconductor quantum wells (J.
Superconductivity/Novel Magnetism, 18, 189-193
(2005))
Previous theoretical studies on III-V DMS
quantum wells have predicted .

• 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.

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Hamiltonian
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(No Transcript)
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Self-Consistent Calculation
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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.

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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.

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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.
T. Dietl et al. PRB 55, R3347(1997) A.H.MacDonald
et al. PRB 61,15606(2000)
M. Tanaka et al . APL 80, 3120 (2002)
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The change of the Tc as a function of the applied
electric fields The change of the fourth power of
the growth direction envelope function of
carriers at the lowest subband.
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.
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Effect of the well width
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.
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3. Model study on the magnetization of digital
alloys (Phys. Rev. B 68, 172406.1-172406.4
(2003))
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.
Model
H. Luo et al., Appl. Phys. Lett. 81, 511 (2002)
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Hamiltonian
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Total magnetization
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The magnetization of digital alloys also
strongly depends on the carrier and Mn ion
concentrations and distribution of Mn ions in
the system.
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Appl. Phys. Lett. 81, 511 (2002)
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
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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
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1. Spin polarized field effect transistor
Suggested by S. Datta and B. Das, Appl. Phys.
Lett. 56, 665(1990)
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Schematic idea of the spin transistor
With a gate voltage V1, spin of electrons precess
with p between two ferromagnets. Expect high
resistance
With a gate voltage V2, spin of electrons precess
with 2p between two ferromagnets. Expect low
resistance
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Requirements for a spin transistor 1. spin
polarizer spin detector (collector) cfgt
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 cfgtSurface states of semiconductor,
2DES----InAs, GaAs spin life time gt 100 ns,
coherent travel distance gt 100 micro m 4.
control of spin precession coherent propagation
of spin
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DMS
DMS
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2. Multi-ferroic materials
Example 1 Mutiferroic BaTiO3-CoFe2O4
nanostructures H. Zheng et al., Science 303,661
(2004).
CoFe2O4-spinel
BaTiO3-perovskite SrTiO3 (001) Substrate By
Pulsed laser deposition
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Example 2 Epitaxial BiFeO3 multiferroic thin
film heterostructures, J. Wang et al.,Science
299, 1719 (2003).
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Multilayer Structures
Diluted Magnetic Semiconductors
(DMS) Ferromagnetic
Ferro-Electric Semiconductors (FES) Ferroelectric
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Quaternary
Dipole Valve
Gate(Au)
FES
FES
FES
DMS
Insulator
Si

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5. Conclusion

• 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.

Thank you for your attention!!!!!