Transparent Electro-active Oxides and Nano-technology

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Transparent Electro-active Oxides and
Nano-technology

• Hideo HOSONO
• Frontier Collaborative Research Center
  Materials and Structures Laboratory,
• Tokyo Institute of Technology, Yokohama, JAPAN

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Schedule of lecture Part (I) Transparent
Oxide Semiconductors

• August 8 Introduction with Grand Prix -awarded
  Movie of
• Transparent Electro-active
  Materials Project
• What is semiconductor /
  transparent oxides ?
• August 9 N-type transparent Oxide
  Semiconductor. electronic structure, application
  as TCOs, material designing for novel N-type TCO,
  and Nano-TCO and applications
• August 10 P-type Transparent Oxide
  Semiconductor material design concept ,
  examples, and devices based on PN-junction
• August 13 Comprehensive understanding of TOS
  viewed from band lineup
• August 14 Thermoelectric oxides and performance
  enhancement utilizing artificial nanostructure
  (Dr.S.WKim of TIT), Exam (I)

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Part II TAOS, C12A7, fs-laser

• August 27 Transparent Amorphous Oxide
  Semiconductors(TAOS) and their application to
  TFTs
• August 28 Nanoporous Crystal 12CaO7Al2O3
• (I) encaging active anions (O?, O2? and H?) and
  their functional properties
• August 29 Nanoporous Crystal 12CaO7Al2O3
• (II) RT-stable electride, their electronic
  properties ( metal-insulator transition,
  metal-superconductor transition) and device
  application
• August 30 Nano-maching of transparent
  dielectrics by femtosecond laser pulse
• August 31 Summary of the lecture and Examination
  (II)

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Energy Diagram
Vacuum level)
Ionization potential
Work Function
Electron Affinity
Conduction band
Conduction Band Minimum
Band Gap
Fermi Level
Valence Band Maximum
Valence band
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What is semiconductor

• ECBM EF kT for N-type
• EF- EVBM kT for P-type

Ncarrier is controllable over several orders
of magnitude by Intentionall doping
W
For Insulator E(band edge) EF gtgtkT
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Electrical Conductivity
Carrier Concentration (cm-3)
Mobility (cm2(Vs)-1)
Effective mass
m t / m
Carrier relaxation time ( inverse of mean free
path)
i.e., depends on quality of sample
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Effective mass m
m ?? dE2/dk2?
m is an intrinsic material property.
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SnO2 crystal structure
Rutile-type structure
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SnO2 band structure
Density of States
CBM
VBM
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Siband structure
CBM
VBM
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Carrier Mobility in various semicond/.
Why is the electron mobility is larger than hole
mobility,?
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Constitution of Liquid crystal displays
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Thin Film Transistor(TFT)
Insulator
Gate
Dorain
Semicond
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LCD Pixel Circuit
(voltage line)
(signal line)
LC
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Thin Film Solar Cells
Superstrate type
glass
TCO(SnO2)
P-type Si
Active pure Si-layer
N-type Si
TCO(ITO)
Metal(Ag, Al)
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Comparison of TCO with metal
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In2O3 crystal structure
CaF2
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ITO(In2O3) electronic structure
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In2O3Sn content and Carrier Conc.
Carrier Conc(1021cm-3)
Sn content(Sn/In) ()
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Plasma Frequency
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Absorption, reflection in TCOs
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Resistivity and reflectance_at_800nm
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Resistivity (Min) vs Year
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Two types of carrier scattering
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Material design for N-type TOS
Edge-sharing MO
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Octahedron Chain
M

p
-block heavy cation
i
e
-
e.g.
In,Ga

2-
ns0
orbital
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SnO2 crystal structure
Rutile-type structure
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SnO2 band structure
Density of States
CBM
VBM
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Various TCOs
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Nano TCOs
Ex. ZnO by Wang (Georgia Tech)
spring
spiral
ring
Nanowire arrays
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Nano power generator
ZnO nanowire
Piezo electric
Wang (Science 2006)
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Electron doping via oxygen vacancy formation
SnO2
Electron becomes mobile, gtcandidate of
transparent metals
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When electron is doped to insulator via oxygen
vacancy formation
Mg2
O2-
O-vacancy
???????