Simple experiment to measure resistance of a semiconductor

[houlahound]

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??

 

[davenn]

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??

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 itDave

 

[houlahound]

So just get a diode connected to an ohm meter and dip it in say ice water, measure then boiling water measure??

 

[BvU]

So just get a diode connected to an ohm meter and dip it in say ice water, measure then boiling water measure??

Just what I was about to propose !

 

[houlahound]

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??

 

[NascentOxygen]

So just get a diode connected to an ohm meter and dip it in say ice water, measure then boiling water measure??

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.

 

[davenn]

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??

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

 

[houlahound]

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??

 

[houlahound]

How do I measure it without getting it wet? Paint it in a sealant??

 

[davenn]

How do I measure it without getting it wet? Paint it in a sealant??

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

 

[houlahound]

Will try this when back at my man den next week and post the results.

Thanks.

 

[NascentOxygen]

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.

 

[LvW]

Will try this when back at my man den next week and post the results.
Thanks.

...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.

 

[houlahound]

K, anyone want to explain what this leakage phenomena is, not something I have heard of.

 

[NascentOxygen]

K, anyone want to explain what this leakage phenomena is, not something I have heard of.

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