Question

In the experiment: To determine the resistivity of the given semiconductor sample by Four Probe method.

Why are there "four" probes instead of 2? what is the mechanism of that four probe setup in relation with the semiconductor that it touches?

Answer 1

An arrangement of the Four Probe is given below.

End of the two probes passes current through the semiconductor and the middle two measures potential difference.

It passes the current through the semi conductor and measure the corresponding voltage across the semiconductor to give an estimate of resistivity of the concerned semi-conductor. This is how the mechanism of Four probe works.

Coming to the question why 4 probes are used instead of two probes, the answer lies within the fact that the four probes cover a larger area of the conductor and hence has less contact resistance and more accuracy. Two probes has less contact area thereby increasing contact resistance and introducing error in the resistivity measurement.

Also the fact that it uses separate probes to pass current and measure voltage is an added advantage because it does not introduce the resistance of the probe itself to our measured values because separate probes are being used. Whereas the same two probes are being used in a two probe method to pass the current and measuring corresponding voltage thereby adding the internal resistance of the probe to our measurement.