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Transparent Electro-active Oxides and Nano-technology

Transparent Electro-active Oxides and Nano-technology. Hideo HOSONO Frontier Collaborative Research Center & Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, JAPAN. Schedule of lecture : Part (I) Transparent Oxide Semiconductors.

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Transparent Electro-active Oxides and Nano-technology

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  1. Transparent Electro-active Oxides and Nano-technology Hideo HOSONO Frontier Collaborative Research Center & Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama, JAPAN

  2. 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.W;Kim of TIT), Exam (I)

  3. Part II TAOS, C12A7, fs-laser • August 27Transparent Amorphous Oxide Semiconductors(TAOS) and their application to TFTs • August 28 Nanoporous Crystal 12CaO・7Al2O3 (I)encaging active anions (O, O2and H) and their functional properties • August 29 Nanoporous Crystal 12CaO・7Al2O3 (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)

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

  5. 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| >>kT

  6. 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

  7. Effective mass m* m*  dE2/dk2 m* is an intrinsic material property.

  8. SnO2 : crystal structure Rutile-type structure

  9. SnO2: band structure Density of States CBM VBM

  10. Si:band structure CBM VBM

  11. Carrier Mobility in various semicond/. Why is the electron mobility is larger than hole mobility,?

  12. source switch（TFT) Liquid crystal Transparent electrode backlite Color filter polarizer polarizer Lighting tubeLED SWITCH（TFT) Constitution of Liquid crystal displays

  13. Souce Gate Dorain Electron path （channel） Gate Voltage Off Gate Voltage On スイッチ・オフ スイッチ・オン source Thin Film Transistor(TFT) Insulator Gate Dorain Semicond

  14. LCD Pixel Circuit (voltage line) (signal line) LC

  15. Thin Film Solar Cells Superstrate type glass TCO(SnO2) P-type Si Active pure Si-layer N-type Si TCO(ITO) Metal(Ag, Al)

  16. Comparison of TCO with metal

  17. In2O3 :crystal structure CaF2

  18. Fan &Goodenough(1977) Energy(eV) Intensity DOS(eV-1) ITO(In2O3): electronic structure

  19. In2O3：Sn content and Carrier Conc. Carrier Conc(1021cm-3) Sn content(Sn/In) (%)

  20. Collective oscillation electron density ne2 wp = 2 eoe m* ∞ Typical metal and ITO Material Plasma Frequency

  21. Plasma frequency Due to VB-CB transition Visible range Reflection due to Carrier electron Absorption due to free carrier Wavelength(mm) Absorption, reflection in TCOs

  22. イオン不純物散乱 scattering due to Ionized impurity Reflectance Resistivity Carrier Conc.(cm-3) Resistivity and reflectance＠８００nm

  23. Resistivity (Min) vs Year

  24. Ionized impurity Scattering ( m i ) Grain boundary Scattering ( mg ) Hall mibility(cm2(Vs)-1 Carrier conc(cm-3) Two types of carrier scattering

  25. Material design for N-type TOS Edge-sharing MO 6 Octahedron Chain M : p -block heavy cation i+ e - e.g. In,Ga 2- ns0 orbital

  26. SnO2 : crystal structure Rutile-type structure

  27. SnO2: band structure Density of States CBM VBM

  28. Various TCOs

  29. Nano TCOs Ex. ZnO by Wang (Georgia Tech) spring spiral ring Nanowire arrays

  30. Nano power generator ZnO nanowire Piezo electric Wang (Science 2006)

  31. Defect-free When oxygens are removed ------- ・ CB is due to metal’s Orbital Excess electrons cannot find stable Sites. Excess electrons are injected Sn4+ O2- Electron Energy Oxygen vacncy Oxygen vacnacy M2+ M2+ M2+ M2+ M2+ M2+ M2+ M2+ M2+ O2- O2- O2- O2- O2- O2- O2- O2- O2- O2- position Free electron Electron doping via oxygen vacancy formation SnO2 Electron becomes mobile, =>candidate of transparent metals

  32. When e- is removed ……… E- becomes immobile （color center）=> remains insulating Defect-free state e- is stabilized by deforming the lattice Electron Enertgy Oxygen vacancy Oxygen vacancy M2+ M2+ M2+ M2+ M2+ M2+ M2+ M2+ M2+ O2- O2- O2- O2- O2- O2- O2- O2- O2- O2- position Trapped electron(color center) When electron is doped to insulator via oxygen vacancy formation Mg2+ O2- O-vacancy 酸素が抜けた跡

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