Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

N-Type semiconductor Silicon

  1. Jan 26, 2005 #1
    In terms of the semiconductor Silicon:

    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

    Adding impurities to metals (which already have loads of conduction electrons) increases their resistivity a little. The impurities just get in the way.

    But the thing about silicon is that without the impurities, there are hardly any conduction electrons, at least at room temp and below. So adding even tiny amounts of a dopant impurity (either an n-type or p-type) reduces the resistivity by orders of magnitude.
  4. Jan 29, 2005 #3

    When you dope silicon with penta-valent atoms, (i.e. n-type semicondoctor) then there will be an excess of electrons. When connect it to a power source, which can be viewed as an electron drain if you're looking from the positive charge, then this will tend to suck the free electrons from the semiconductor, and of course, the negative end which can be viewed as an electron sourse, will supply the semiconductor with the electrons needed for continuous 'sucking'.

    For p-type, tetra-valent doping will creat a hole, which can be simply viewed as a positive charge. So when you connect it to a power supply, then electrons supplied from the negative end, will fall in the hole, and the pushed to the other end by the stream of electrons to be re-collected at the positive end of the source.

    Hope i was clear :rolleyes:
  5. Feb 9, 2005 #4

    I was more going on the point that there is an open hole instead of an electron floating around in the p-type. Since ther is a whole, electrons would more likely be able to conduct better. However in the n-type, there is a bound electron put there by the impurity. Thus electrons that are being brought from a power source have to fight that electron. :approve:

    Or else i'm being stupid.

    I thought electrons liked to use other electrons holes as a pathway to getting somewhere faster. :grumpy:

    Kinda like in sonic the hedgehog where you go through a speed door and you get a super speed boost to get done with the level faster. You could use the n-type which is not take the speedwarp door and fight through the badguys which is the bound electron put there by the impurity, or else you could take the p-type which would have less resistance and a speed door that gives you a boost and less badguys to fight. :tongue:

    eh. :yuck:

    So basically. There is resistance added because of the impurity. But my question was. Which would be more resistant: N-type or P-type?
    Last edited: Feb 9, 2005
  6. Feb 9, 2005 #5


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Having more electrons in the conduction band (which is what adding an N-type impurity does) or more holes in the valence band (from P-type dopants) only increases the conductivity. Your understanding of electron transport is a little off. The model that explains semiconductors well assumes that there is virtually no interaction between the electrons themselves, and it turns out that this is a good assumption to make. As a result, the conductivity is linearly proportional to the number of free charge carriers (per unit volume).

    So in fact doping increases conductivity and reduces resistance, irrespective of whether it's N- or P-type.

    Moral : Electron transport does not work like Sonic.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook