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P and N?

  1. Oct 29, 2004 #1

    Mk

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    What are, and the diffrences between p and n type materials?
     
  2. jcsd
  3. Oct 29, 2004 #2
    it's been a while since my last solid state physics course, but I think the primary distinction is whether the charge carriers are positive (p type) or negative (n type).

    someone else might correct me with a better answer.
     
  4. Oct 29, 2004 #3
    If this is with reference to semiconductors,

    Semiconductors are materials whose conductivity is between those of well known conductors and insulators. This conductivity can be increased and one way is doping, that is, putting an impurity in the structure of the semiconductor material.

    If the doping is such that it causes an increases the number of electrons in the semiconductor, it is called a n-type semiconductor and if it causes a deficiency of electrons, then it is called a p-type semiconductor. (in this case, conduction takes place with the help of "holes" caused by electron deficiency)



    spacetime
    www.geocities.com/physics_all/index.html
     
  5. Oct 29, 2004 #4

    Gokul43201

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    If you dope N, P, As (each of which has 5 valence electrons), or even S, Se, Te (6 valence electrons) in a semiconductor (like Si, which has 4), then you provide an excess electron per dopant atom. This kind of doping causes the conductivity of the semiconductor to be a strong function of the number of excess electrons. This doped semiconductor is referred to as N-type.

    On the other hand, if you dope with Ga, Al, In, (3 valence electrons) or even Mg, Be, Zn (2 valnce electrons), you create a deficiency of one electron per dopant atom - also called a hole. In such materials where the conductivity is a strong function of the hole concentration, the material is called P-type.
     
  6. Oct 29, 2004 #5
    Some of what you need to know about semiconductors:

    Britney Spear's School of Solid State Physics

    I also recommend the The Art of Electronics by Horowitz for a much simpler explanation.
     
    Last edited: Oct 29, 2004
  7. Oct 29, 2004 #6

    ZapperZ

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    imabug gave the most accurate answer, at least from my perspective. n-type and p-type simply refers to the type of the majority carriers in ANY material, IRREGARDLESS of how it got that way.

    If the material happens to be a semiconductor, then the most common (but NOT the only way) to change the "type" is via doping. However, semiconductors like GaN, for example, are naturally one type (I think it's naturally n-type, but I can't be sure) without being doped.

    The same with the cuprate superconductors. One can either dope it with electrons (n-type superconductors like NdCeCuO), or dope it with oxygen/holes (p-type superconductors such as YBCO, BSCO, etc).

    Zz.
     
  8. Oct 29, 2004 #7

    pervect

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    N type semiconductors have electrons as the primary charge carriers. P type semiconductors have "holes" as the primary charge carriers. If one examines the momentum vs velocity curve of an electron in the uppermost energy band of a p-type semiconductor (the band that is responsible for current flow through the semiconductor as a result of applied fields), one finds that such electrons in such a semiconductor have a negative effective mass.
     
  9. Nov 20, 2004 #8
    I have had big problems with finding help for this, in case the sight he showed you didn't help you, I will. Transistors are electricly-controlled switches. There's a base, a collector, and an emitter. Basicly, you put a small voltage on the base, and it closes the switch.
    HOW!!!
    I don't know how much you know about diodes, so I will explain the whole thing. A semiconductor is a material that is not an insulator nor is it a conductor, it's kind of in between. A diode is a one way gate for current, this means if current is going the wrong direction, it will not let it passed, but if it is going the right direction, it will pass. Silicon has a total of 4 valence electrons. Valence electrons are kind of electrons that are swapped between atoms, so the atom can be more stable. To understand this much better go into atoms, molecules, and matter, and take a look at my valence electrons post. Okay...a silicon, a common element used for semiconductors, has 4 neighbors it shares valence electrons with. There are no extra electrons in the lattice of silicon, and this makes electrical resistance high. So, in the lab - where the diode is made - aluminum is injected into the silicon. Aluminum has 3 valence electrons, so it can't make a connection to one of the silicon atoms, because it only has three to share. Imagine a lattice of interconnected lines. At the intersections of the lattice there are dots, these are atoms. When you look at it, one of these dots connect with 4 other atoms through the extending lines. Well, aluminum is like a dot on that lattice that does not have a fourth protruding line, so it is not connected to that atom. This is because it only has 3 valence electrons to share. So, in order to fill it's valence shell to 8 - which it will never get, but trys to get as close as possible - it steals an electron. You're saying, hey where did 8 come from, well to understand why a valence shell is filled with 8 valence electons you need to go to where I told you to go earlier. Anyway, it steals an electron from the neighboring silicon atom - SOME NEIGHBOR!!! this causes the neighboring silicon atom to only have 3 valence electron, so it still it from the next silicon atom, causing this one to steal, and so on...GEEZE, THEY'RE ALL A BUNCH OF LOOTERS!!! Alright this lack of an electron is what we in electronics like to call a whole. Now, to help clarify a little bit, imagine chineese checkers. You have a bunch of indents with marbles filling them in, but one indent is missing a marble - let's call that the whole. Move the marble left of the indent into the indent, then move the marble left of that one to fill the new one. See the process? The indent is, in a way, moving to the left. the marbles are the valence electrons, this is, basicly, what happens. This part of the silicon is called N, for negative, because there is MINUS one electron.
    Now, that we got that cleared, lets take another piece of silicon and add phosphorous to that. Phosphorous has 5 valence electrons, so it combines with all four of the silicon atoms. WAIT A MINUTE, that adds to 9 valence electrons, that can't be right!!! The final valence electron is, basicly, ejected, and is just floating around, so it adds to 8, whoo!!! This part of the silicon is called P, for positive, because there is PLUS one electron.
    Okay...Now that were a done with the hard part, to the easier part...we take the silicon pieces, and sandwhich them togethe, TADA!!! At the joint where the P and N silicons meet, there is something happening. The atoms are swapping electrons, the looters on one side are accepting electrons from the phosphorous on the other side, making them even. It's like this imagine a POOR community, and there is a RICH community, now when the neighborhoods meets, the RICH give electrons - money - to the POOR, and now they are all middleclass. If only that's how it worked in real life!!! Okay... So at the juction where the P and N meet, they are now even, no wholes, no extra electrons, but remember, this is only at the junction, the rest of the silicon is still RICH and POOR. Okay...This conjuction is no longer conductive, it is now an insulator!!! This insulator is called the depletion zone.
    So, what we do is hook a battery up, electrons flow from the negative side of a battery, unless you use conventional current, and WHY you would use that I don't know. Anyway...as current flows from the negative side of a battery, if it in connected to the N side of the the "DIODE" - that's right it is a diode - the wholes are attracted to the free electrons, they are not really attracte, it's just the wholes - or lack of electrons - kind of "moves" torwards the conjustion where the wire connects to it. This causes all the wholes to move torwards the wire, and away from the P - N conjuction. This causes the depletion zone to widen, and more resistance, basicle, it's an even bigger insulator. We call the diode reverse-biased. Okay...a bigger insulator, that has more resistance, and almost so much no current could flow through that!!! So, we change the battery around, the Positive is connected to the aluminum, and the negative is connected to the phosphous. This is called forward-biased. The electrons from the battery flow into the phosphorous silicon, causing the extra electrons to be repelled, LIKES REPELL!!! And on the aluminum the same happens. This causes the wholes and the electrons to be repelled from the wire conjuction, and reduces the depletion zone. Eventually, when 0.7 volts is applied the depletion zone, basicly, deminishes, and the diode conducts current. Wow!!!
    TRANSISTERS.
    Now, a transistor has two possible configurations, NPN or PNP. This is, simply, the configuration of the aluminum and phosphorous. Let's use NPN. Okay...three volts is applied to the emitter, 2.3 volts must be on the base, and the collector goes to positive, through a light bult. The positive 0.7 volts in respect to the emitter, because the center is P. This causes the depletion zone between the base and the emitter to diminish, allowing current to flow through the base. Then, the emitter has to be, 0.7 volts, so that it can diminish the collector's depletin zone, this causes current to flow from the emitter to the collector. We can now add as much voltage to the emitter as we want, and therefor make an electronicly-controlled switch.
    WHOO, I hope you learn something from this, because it took me an hour to type, but...I had fun.
     
  10. Nov 20, 2004 #9

    Mk

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    WOW! Thanks a lot! That was great!
     
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