| Conductivity measurements (I-V measurements) at RT
A. Principle of the method
We apply the van der Pauw technique to deduce the sheet resistance RS. The principle of the measurement is shown below:
RA and RB are related to the sheet resistance through the van der Pauw equation:
exp(-πRA/RS) + exp(-πRB/RS) = 1
To obtain the two characteristic resistances, one applies a dc current I into contact 1 and out of contact 2 and measures the voltage V43 from contact 4 to contact 3 as shown above. Next, one applies the current I into contact 2 and out of contact 3 while measuring the voltage V14 from contact 1 to contact 4. RA and RB are then
RA = V43/I12 and RB = V14/I23
This equation can be solved numerically for RS. The bulk electrical resistivity can be calculated using
ρ = RS d
where d is the film thickness.
B. Experimental setup
The experimental setup is shown in the figure below:
The electronic circuit consists of a Keithley M. 6220 DC current source and a Keithley Mo. 2182 Nanovoltmeter. Both instruments are connected to a pC via an IEEE-488 interface.
The home-made sample holder consists of 4 spring probes that are mechanically pressed of the thin film sample. The probes form a quadrant with side length 10 mm (minimum sample dimensions).
C. Example
The I-V measurement is presented for a PLD grown NiO thin film with the following deposition parameters:
Glass substrate temperature 200 oC
Oxygen pressure 10 Pa.
 
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