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Good dielectric yet hole conductor?

  1. Mar 2, 2013 #1
    Is there some material that could withstand relatively high voltages before it starts to conduct electrons,but in the same time a good hole conductor?
    Could such material be obtained by doping some dielectric similar to SiO2?
  2. jcsd
  3. Mar 3, 2013 #2


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    Good hole conductors are good electric conductors.
    p-doped semiconductors are good hole conductors.
  4. Mar 3, 2013 #3
    An aluminum wire is a good hole conductor. It contains no conduction-electron while it is a solid wire. However, if you pass enough electricity through it, it will explode and turn into an aluminum plasma. Then it will conduct by means of positively charge ions, negatively charge ions, and free electrons.

    Is this what you wanted?
  5. Mar 3, 2013 #4


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    Nonsense. Aluminum contributes about 3.5 electrons per atom to the conduction band.
  6. Mar 3, 2013 #5


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    A dielectric is insulating by definition. You are asking questions here that shouldn't be asked here before you have done a tiny bit of research.
  7. Mar 3, 2013 #6
    What is the sign of the Hall coefficient in Al?
  8. Mar 3, 2013 #7


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    Ok, I'll moderate my comment to "it depends." As usually measured at high fields, which are used to get a large Hall voltage, it is positive. When measured carefully at near-zero fields it's negative--at least at low temperature, where I'm familiar with it.
  9. Mar 3, 2013 #8
    Something that conducts holes well,but doesn't conduct electrons even at high voltages.
  10. Mar 3, 2013 #9


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    Fine, but that's still not a dielectric.
  11. Mar 5, 2013 #10
    Aluminum at room temperature and higher.

    I don't know about the cryogenic properties of aluminum. One poster claimed that aluminum has conduction electrons at very cold temperatures.

    I just know about the Hall coefficient at room temperature. That Hall coefficient is positive and large at room temperature. Therefore, aluminum at room temperature is a very good hole conductor. Aluminum at room temperature is not an electron conductor.

    Aluminum is inexpensive, very available, nontoxic and malleable. Aluminum foil can be bought in supermarkets. Using a file and a bar of aluminum, one can make aluminum powder. Hardware stores can supply flat plates and bars of aluminum. Some chemistry supply houses sell bottles of aluminum powder.

    Aluminum wire used to be widely available, but is less available now. Aluminum wiring was used in homes. Aluminum turned out to be a fire hazard in homes. Now, aluminum wiring in homes is unavailable. However, I think aluminum wire is still available by mail. It has specific purposes outside the home.

    Here are a few articles on aluminum at cryogenic temperatures. Aluminum does make a transition from being a hole conductor to being an electron conductor at a temperature well below room temperature. However, at room temperature aluminum is a hole conductor.

    This is a link to an abstract. The article is behind a pay wall.
    “A study has been made of the true low field Hall coefficient, RH, of four samples of pure aluminium between 4.2 and 77K. All samples exhibited a low-temperature maximum in the temperature range 7-10K and the three purest samples possessed a minimum between 25 and 30K. An analysis of the low-temperature results is given using a three group model. It is found that, despite the dominance of impurity scattering, the low-temperature maximum may be explained if the mean free paths due to phonon scattering of second-zone holes and third-zone electrons have different temperature dependences.”

    Here is an article on aluminum-zinc alloys at close temperature.
    “4.2 K and 77 K. At both temperatures, R_H changes from negative to positive values with increasing Zn contents.”

    Is aluminum at room temperature what you wanted? If not, why not?
    Last edited: Mar 5, 2013
  12. Mar 6, 2013 #11
    Wrong.Aluminum does have negative hall coeficient.And those metals which have positive Hall coefficient are not necessarily conduct only holes at room temp.Probably they conduct electrons too,but just slightly less then holes.If you want to prove something different, give a link.
  13. Mar 7, 2013 #12
    In Ashcroft and many popular solid state books the charts are given in terms of NEGATIVE Hall coefficients, so you are looking at the chart wrong. Al indeed has a positive Hall coefficient.

    Also you are confusing "not conducting electrons" with "dielectric". Dielectrics don't really conduct with either electrons or holes at any temperature at which they are solid. At most they have ionic conduction at high temperatures as several ceramics and polymers do.
  14. Mar 7, 2013 #13
    Look at this.Though there could be few allotropic forms of aluminum.
    Not at all.I just theoretized if good hole (but not electronic) conductor could be obtained by
    doping dielectric with p-type dopant.
  15. Mar 7, 2013 #14
    Thank you for correcting me. My source may have been (probably been) mistaken.

    Moderators, please forgive me!

    There is a very odd discrepancy for the Hall coefficient in my sources. There is probably some convention that changed.

    First, I took the Hall coefficient from my favorite book on solid state physics:
    “Introduction to Solid State Physics”, 7th ed. by Charles Kittel (Wiley, 1996) p167

    There is no link to Charles Kittel’s book. However, I may have to buy a new book on solid state physics because of this mistake of Kittel’s.

    On page 167, there is a table with Hall coefficients in CGS units. The value of the Hall coefficient is:
    The number of free carriers per atom is also calculated in the metals. For aluminum, the table says that there is 1 hole per atom of aluminum.

    Moderators, please note. I was quoting directly from Charles Kittel, which is considered a very good textbook on solid state physics. I did not make this “fact” up. I looked it up. If there is a mistake, it was from Charles Kittel. Please forgive me!

    Now, I have a link
    http://disse.org.br/LabsemCursos/uploads/Materiaiseletricos/HallEffect,3Ed.pdf [Broken]
    The value of the Hall coefficient is:
    -3.5x10^-11 m^3A^-1 s^-1.

    I found still another link that says the Hall coefficient that says that the Hall coefficient changes with field strength.
    “A number of materials show a striking difference between the weak and strong field limits; aluminum is one.”

    I didn’t know about this difference between field limits. I don’t know which is Kittel’s but I was going by that. I wonder if this is what the OP wanted.

    So this is interesting. I hope someone explains how the field strength changes the Hall coefficient of aluminum.

    There may also be a matter of allotropes. I don't know if solid aluminum comes in different phases. Maybe one phase has valence-hole carriers and one phase has conduction-electron carriers.

    Never the less, this is Kittel's error. Moderators, please don't kick me off for this. A reputable source did tell me that aluminum is a hole conductor.
    Last edited by a moderator: May 6, 2017
  16. Mar 7, 2013 #15
    Yes. This type of material is called a "semiconductor crystal".

    The word "semiconductor" does not refer to a material that always has a mediocre conductivity. The word "semiconductor" refers to choice. One can choose the both the conductivity and the type of conductivity of a semiconductor crystal by changing certain conditions.

    An electrical insulator is a dielectric. Even a semiconductor crystal can be a dielectric. A semiconductor crystal with high-conductivity is sometimes called a semi-insulating crystal. There are several ways of growing a semi-insulating crystal.

    A pure (i.e., "extrinsic") semiconductor crystal with a medium to large band gap is an insulator (i.e., dielectric). One grow the same type of crystal which has a low resistivity (i.e., a conductor) two ways. If you add an n-dopant, the crystal is a conduction-electron conductor. If you add a p-dopant, the crystal is a valence-hole conductor.

    A semiconductor crystal does not have to be pure to be a dielectric. One can grow a compensated crystal by adding almost equal amounts of n-dopant and p-dopant. One can also add a lot of deep-level impurities to take away the free-carrier. I am studying one type of compensated, semi-conducting crystal now.

    One can add carriers to a semiconductor by shining light on it. Light can generate free-carriers. This is called photoconductivity.

    In the case of a compensated semiconductor, you may be able to control the type of free-carriers by tuning the frequency of the light. By changing the frequency, you can excite different impurities.

    Therefore, I suspect that you are using a definition for dielectric that the rest of us don't know. How do you define "dielectric"?
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