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Can electron stay between donor energy level and valence band?

  1. Nov 17, 2012 #1
    In n-type semiconductor, Can electron stay between donor energy level and valence band?
    Can I say that the donor energy level here refer to the Fermi level?

    Thank you
  2. jcsd
  3. Nov 17, 2012 #2
    No, donor energy level is different than fermi level. Donor energy level is fixed w.r.t other energy levels (like 0.01 eV below conduction band). But fermi level varies after equilibrium is reached (like after dopant insertion and equilibrium fermi level will rise up).

    Everything b/w conduction and valence band is forbidden except donor and acceptor levels. So, electrons can only stay in donor or acceptor levels if b/w conduction and valence bands. (if defect/surface/recombination states are ignored)
  4. Nov 17, 2012 #3
    Thank you
    Then in n-type semiconductor , there will be conductn band ,valence band , donor energy level and Fermi level at the same time?
  5. Nov 17, 2012 #4
    Yeah, four of them will be there. But, remember the fermi level, itself, does not designate any energy level(slot) where electrons can reside. Its just a reference line which determines how electrons will be populated.
  6. Nov 17, 2012 #5
    You make this statement because Fermi level is a level that has a probability of 50% to be occupied by electrons at any given temperature?

    And one more: electrons of intrinsic semiconductor can't stay at energy gap except Fermi level ?
  7. Nov 17, 2012 #6
    You're confusing fermi level with energy level. Fermi level is not an energy level as it cannot hold any electron. Its a reference line which determines electron occupancy. Occupancy means probability of presence of electron IF there is an energy level ALREADY present. So even if fermi level is lying inside forbidden energy gap, no electron will be present in it.

    electrons of intrinsic semiconductor can't stay anywhere inside the energy gap.
  8. Nov 17, 2012 #7
    In intrinsic semiconductor, the energy level ALREADY present refers to the conduction and valence band ,right?
  9. Nov 18, 2012 #8
    Yeah. That's right.
  10. Nov 18, 2012 #9
    Thanks a lot.
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