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Question about semiconductors' holes.

  1. Sep 19, 2011 #1
    I know holes are made/present after electron leaves its place but are holes present in metals during photo electric effects???

    what is the mass of a hole (if it has any)?

    what are its characteristics are they exactly opposite of electron ( i mean its behaviour in electric and magnetic field ) ?
     
  2. jcsd
  3. Sep 20, 2011 #2
    When calculating the dynamics for a crystal in an applied field, you need to include the contribution from every band. Using a derivation from solid state which I can't quote exactly, you can show that you can solve for the motion by considering the evolution of the occupied states (the electrons), or equivalently, the unoccupied states (the holes). You choose one convention for each band because otherwise you would be counting twice. Conceptually, the holes are only useful in the valence band where almost all states are occupied. But if you wanted to, you could treat the conduction band as a huge number of holes as well.

    In the normal usage, holes are in the valence band and electrons are in the conduction band. Their properties depend on the band structure, and in general, will not be exact opposites of eachother. Electrons and holes can have very different effective masses in some materials.
     
  4. Sep 20, 2011 #3
    Gravitational or inertial?
     
  5. Sep 20, 2011 #4
    A "Hole" typically refers to a vacancy left in the valence band that is mobile yet localized, so that it acts as an effective positively charged object free to move around and carry current. If the photon in the photoelectric effect knocks an electron out of the valence band (typical in semiconductors), then, yes, it will leave a hole. This effect is used in photodiodes. If the photon knocks a conduction electron (as is abundant in metals) out of the material, it does not leaves a hole, because the vacancy it leaves behind is not localized and does not act as a pseudo-particle.

    It depends on the material. The hole is assigned an effective mass based on how it moves about under forces, which differs by material. For instance, Silicon has a heavy hole effective mass of 49% the mass of a totally free electron.

    Holes are positively charged and have different masses than electrons. This means they will flow the opposite direction as electrons under an applied field.
     
  6. Sep 20, 2011 #5
    THnax chrisbaird but what do u mean by "mobile yet localized"
     
  7. Sep 21, 2011 #6
    Localization means that an electron/hole is associated with an atom/molecule. Don't quite get what is mobile + localized.
     
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