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Metals in Contact with Si for Schottky or Ohmic Contacts

This exercise discusses the energy diagram for Schottky and Ohmic contacts in Si semiconductor devices. It provides the parameters and conditions for determining the type of contact formed with different metals.

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Metals in Contact with Si for Schottky or Ohmic Contacts

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  1. Semiconductor Devices 26 Atsufumi Hirohata Department of Electronics 11:00 Tuesday, 2/December/2014 (P/T 006)

  2. Exercise 5 State the following metals in contact with Si to form either Schottky or Ohmic contacts based on their energy diagram. Assume the following parameters: Si electron affinity: c = 4.05 eV and Si bandgap: Eg = 1.11 eV.

  3. Answer to Exercise 5 The electron affinity is defined as For an n-type contact, : Ohmic contact : Schottky contact with the barrier height of For an p-type contact, : Ohmic contact : Schottky contact with the barrier height of

  4. Answer to Exercise 5 n-type semiconductor Metal

  5. 26 Schottky Junction • Image force • Schottky effect • Depletion layer capacity • Ohmic contact

  6. Schottky Barrier Definition of energy at the Schottly barrier : c * S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 2006).

  7. Image Force Origin of image force : Metal (M) Vacuum Force between the two electrons : * S. Kishino, Physics of Semiconductor Devices (Maruzen, Tokyo, 1995).

  8. Image Force at a Metal Semiconductor Interface Potential energy for an electron : Image force at a metal semiconductor interface : Vacuum level Vacuum * S. Kishino, Physics of Semiconductor Devices (Maruzen, Tokyo, 1995).

  9. External Electric Field Application Under an electric field E : Schottky barrier at a metal semiconductor interface : Vacuum level Vacuum Schottky effect * S. Kishino, Physics of Semiconductor Devices (Maruzen, Tokyo, 1995).

  10. Metal - Semiconductor Junction Realistic energy diagram of a Schottky junction : Junction Under a forward bias application : Under a reverse bias application : * S. Kishino, Physics of Semiconductor Devices (Maruzen, Tokyo, 1995).

  11. Depletion Layer Capacity q(Vbi + VR ) qVR EC EF Depletion layer EV Electric field distributions w x Potential distributions Vbi + VR w x Under reverse bias, Poisson’s equation is defined as where the donor density is assumed to be constant. Here, the boundary conditions are at at Charge distributions Therefore, the depletion layer width w can be determined by qND w x Depletion layer capacity C is * www.tc.knct.ac.jp/~hayama/denshi/chapter3.ppt

  12. Ohmic Contact By highly doping an interfacial region : Vacuum level Vacuum level Metal Highly doped semiconductor Semiconductor Junction * S. Kishino, Physics of Semiconductor Devices (Maruzen, Tokyo, 1995).

  13. Realistic Schottky Barrier Image force and Shottky barrier : * S. M. Sze, Physics of Semiconductor Devices (Wiley, New York, 2006).

  14. Exercise 6 q(Vbi + VR ) qVR EC EF Depletion layer EV Calculate the depletion layer capacity at a reverse bias VR = 0.5 V in a Au/n-Si Schottky diode. Assume the following parameters: Au work function: fM = 4.80 eV n-region: doping density of ND = 1  1021 m-3 Si electron affinity: c = 4.05 eV Si Fermi level: EF = EC – 0.15 eV permittivity: e = ee0 = 12.0  8.854  10-12 F/m and q = 1.6  10-19 C.

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