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ECE 480 – Introduction to Nanotechnology + Lab.

ECE 480 – Introduction to Nanotechnology + Lab. Emre Yengel Department of Electrical and Communication Engineering Fall 2013. Silicon; Basics. Silicon; Basics. Silicon; Basics. Silicon; Basics. Silicon; Basics. Silicon; Basics. Silicon; Basics. Silicon Wafer. Silicon Wafer.

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ECE 480 – Introduction to Nanotechnology + Lab.

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  1. ECE 480 – Introduction to Nanotechnology + Lab. Emre Yengel Department of Electrical and Communication Engineering Fall 2013

  2. Silicon; Basics

  3. Silicon; Basics

  4. Silicon; Basics

  5. Silicon; Basics

  6. Silicon; Basics

  7. Silicon; Basics

  8. Silicon; Basics

  9. Silicon Wafer

  10. Silicon Wafer

  11. Silicon Wafer • Czochralskisi crystalgrowth;

  12. Silicon Wafer • 1-inch (25 mm) • 2-inch (51 mm). Thickness 275 µm. • 3-inch (76 mm). Thickness 375 µm. • 4-inch (100 mm). Thickness 525 µm. • 5-inch (130 mm) or 125 mm (4.9 inch). Thickness 625 µm. • 150 mm (5.9 inch, usuallyreferredto as "6 inch"). Thickness 675 µm. • 200 mm (7.9 inch, usuallyreferredto as "8 inch"). Thickness 725 µm. • 300 mm (11.8 inch, usuallyreferredto as "12 inch"). Thickness 775 µm. • 450 mm (17.7 inch, usuallyreferredto as "18 inch"). Thickness 925 µm (expected)

  13. Silicon; Defects

  14. Silicon; Defects

  15. Semiconductors • Low resistivity => “conductor” • High resistivity => “insulator” • Intermediate resistivity => “semiconductor” • conductivity lies between that of conductors and insulators • generally crystalline in structure for IC devices • In recent years, however, non-crystalline semiconductors have become commercially very important polycrystalline amorphous crystalline

  16. Semiconductor Materials

  17. Band Theory of Solids • The conduction band is the range of electron energies enough to free an electron from binding with its atom to move freely within the atomic lattice of the material as a 'delocalized electron'. • In solids, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature.

  18. Silicon; Defects • Atomic density: 5 x 1022 atoms/cm3 • Si has four valence electrons. Therefore, it can form covalent bonds with four of its nearest neighbors. • When temperature goes up, electrons can become free to move about the Si lattice.

  19. Electrical Properties of Silicon  Silicon is a semiconductor material. • Pure Si has a relatively high electrical resistivity at room temperature.  There are 2 types of mobile charge-carriers in Si: • Conduction electrons are negatively charged; • Holes are positively charged.  The concentration (#/cm3) of conduction electrons & holes in a semiconductor can be modulated in several ways: • by adding special impurity atoms ( dopants ) • by applying an electric field • by changing the temperature • by irradiation

  20. Silicon; Electron-Hole Pair Generation • When a conduction electron is thermally generated, a “hole” is also generated. • A hole is associated with a positive charge, and is free to move about the Si lattice as well.

  21. Carrier Concentration in Intrinsic Silicon • The “band-gap energy” Eg is the amount of energy needed to remove an electron from a covalent bond. • The concentration of conduction electrons in intrinsic silicon, ni, depends exponentially on Egand the absolute temperature (T):

  22. Silicon; Defects

  23. Silicon; Doping (N type) • Si can be “doped” with other elements to change its electrical properties. • For example, if Si is doped with phosphorus (P) (or arsenic (As)), each P atom can contribute a conduction electron, so that the Si lattice has more electrons than holes, i.e. it becomes “N type”: Notation: n = conduction electron concentration

  24. Silicon; Doping (P type) • If Si is doped with Boron (B), each B atom can contribute a hole, so that the Si lattice has more holes than electrons, i.e. it becomes “P type”: Notation: p = hole concentration

  25. Summary of Doping

  26. Silicon; Electron-Hole Concentrations • Under thermal equilibrium conditions, the product of the conduction-electron density and the hole density is ALWAYS equal to the square of ni: N-type material P-type material

  27. Terminology donor: impurity atom that increases n acceptor: impurity atom that increases p N-type material: contains more electrons than holes P-type material: contains more holes than electrons majority carrier: the most abundant carrier minority carrier: the least abundant carrier intrinsic semiconductor: n = p = ni extrinsic semiconductor: doped semiconductor

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