Semiconductor Doping

Discussion in 'Homework Help' started by Jess_88, Oct 18, 2011.

  1. Jess_88

    Thread Starter Member

    Apr 29, 2011
    174
    1
    Hey guys. :)

    I'm a little confused as to how my teacher came in his conclusion on these question.

    Question:
    Silicon is doped with 5 × 10^16 arsenic atoms/cm3. (a) Is the material n- or p-type? (b) Calculate the electron and hole concentrations at T = 300 K

    Ans
    a)
    n-type
    b)
    ni = 1.5 x 10^10
    no = Nd = 5 × 10^16 cm^-3
    po = 4.5 x 10^3 cm^-3


    I understand how to do part b), but its determining if its n-type or p-type thats got me confused.
    From what I understand
    if no<po, then it is p-type
    if no>po then it is n-type
    but we only have ni and (Nd or Na)...

    Question:
    A silicon semiconductor material is to be designed such that the majority carrier electron concentration is no = 7 × 10^15 cm^−3 . Should donor or acceptor impurity atoms be added to intrinsic silicon to achieve this electron concentration?
    What concentration of dopant impurity atoms is required?

    Ans:
    Donor
    Nd = 7 × 10^15 cm^−3

    Is this because an intrinsic material requires no = po = ni?

    thanks guys :)
     
  2. Zazoo

    Member

    Jul 27, 2011
    114
    43
    Arsenic is a Group V element (donor), so doping with it creates n-type Silicon.
     
    Jess_88 likes this.
  3. Jess_88

    Thread Starter Member

    Apr 29, 2011
    174
    1
    ah cool. So what is the result of doping with Group III or IV?
     
  4. Zazoo

    Member

    Jul 27, 2011
    114
    43
    Group III are acceptors - the missing 4th valence electron creates an extra hole per each dopant atom added. So it would be p-type.

    I don't know what the benefit of doping with Group IV atoms would be as this wouldn't change the balance of electrons/holes in the semiconductor (silicon itself is Group IV.) But, I'm far from an expert, so maybe another member can chime in here.
     
    Jess_88 likes this.
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