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Homework Help: N/P-Type structures.

  1. Jan 26, 2005 #1
    N types have on more free electron added to its structure from doping an impurity on it. Such as an arsenic impurity onto a pure intrinsic silicon crystalline structure.

    However wouldn't it having one more electron inside of it that is bound to the arsenic atom make the ntype more resistant to electron flow from a power source with an emf/voltage/potential difference?

    I also wonder about the vice versa for the P-type.

    Wouldn't the P-Type be more conductive unlike the N-Type which i am assuming to be resistive?

    Mainly because when doping something onto a silicon structure to make it a N-Type a hole is created. Thus allowing electrons to want to take that hole for transportational use.
  2. jcsd
  3. Jan 26, 2005 #2


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    Well, I do not quite understand what your problem is.

    When you add impurity atoms to the silicon, they are built into the crystal, they just occupy the place of Si atoms. The crystal stays neutral, but acquires loosely bound electrons when the impurity is a donor with higher valence than Si. These loose electrons are exited at relatively low temperatures already. They leave their parent atoms, and can migrate freely in the crystal.
    On a similar way, introduction of a 3-valence impurity (acceptor) means a missing electron from a bond: this empty place can migrate around in the crystal and we call this empty place "hole".
    Conductivity increases when the number of free carriers increase in the crystal. If the concentration of the free carriers is very high there can be an opposite effect because of scattering among each other. This effect would increase the resistance.
    If there are both acceptors and donors in a region, as it is near a p-n junction the free electrons and free holes would "recombine" making a "depleted region" near the junction, which is free from charge carriers, but having static charge distribution. This charge distribution produces a potential gap for further transport of electrons to the p type side and holes to the n type side across the junction.

    Was it that you wanted to ask?

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