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Simple experiment to measure resistance of a semiconductor

  1. Mar 25, 2016 #1
    Unlike Ohmic resistors the resistance of a semiconductor decreases with temperature...or not.

    Can a fragment chipped off a diode or some random IC be used to measure this with a multi meter??
     
  2. jcsd
  3. Mar 25, 2016 #2

    davenn

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    that would be very difficult as you would need to get both the P and N materials together
    easier just to keep the diode in one piece and measure across it


    Dave
     
  4. Mar 25, 2016 #3
    So just get a diode connected to an ohm meter and dip it in say ice water, measure then boiling water measure??
     
  5. Mar 25, 2016 #4

    BvU

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    Just what I was about to propose !
     
  6. Mar 25, 2016 #5
    I'm skeptical its that easy.

    I don't know if a diode has a temp coefficient per we but will the differences in ihms even be noticeable on a hobby multimeter??
     
  7. Mar 25, 2016 #6

    NascentOxygen

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    The diode's V-I curve is temperature dependent. So the voltage varies if you change the current and also if you change the temperature. So the best arrangement for use as a thermometer would be to, say, fix current constant and measure the changes in V with temperature.

    Nevertheless, an ohm meter will show a change in its reading. Water on the device may introduce a parallel resistive path.
     
  8. Mar 25, 2016 #7

    davenn

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    it is that easy, seriously!! ... but don't try and measure when the diode is wet, there's going to be leakage through the moisture

    Diodes are commonly used for temperature sensing on heat sinks of power amplifiers audio and RF types

    Dave
     
  9. Mar 25, 2016 #8
    Thanks, I was hoping to avoid a indirect I-V measurement and wanted to measure the resistance ifvthe "dead" material directly.

    Silicon or germanium diode??
     
  10. Mar 25, 2016 #9
    How do I measure it without getting it wet? Paint it in a sealant??
     
  11. Mar 25, 2016 #10

    davenn

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    you could dip it in epoxy, silicone sealer or yes, even paint ... which ever you use ... obviously, let it dry first :)


    Dave
     
  12. Mar 25, 2016 #11
    Will try this when back at my man den next week and post the results.

    Thanks.
     
  13. Mar 25, 2016 #12

    NascentOxygen

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    Drop diode & leads into a plastic bag and just don't immerse the opening. For hot temperatures, I'd try an oven bag, it's probably a good electrical insulator. Test with meter.
     
  14. Mar 25, 2016 #13

    LvW

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    ...and don`t forget that the diode has a non-linear V-I characteristics which means that you always have to discriminate between the STATIC (DC) and DYNAMIC (AC) resistance.
     
    Last edited: Mar 25, 2016
  15. Mar 25, 2016 #14
    K, anyone want to explain what this leakage phenomena is, not something I have heard of.
     
  16. Mar 25, 2016 #15

    NascentOxygen

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    Just says that some current will go through the water instead of through the diode, causing the meter to give a misleading reading.
     
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