Hi, I'm studying the electrical properties of amorphous SiC.
I have plotted the I-V curve using data coming from a 4 probe configuration on a TLM structure: the two probes for voltage measurement are in 2 contact pads distant 70micron and the other 2 probes for current injection are in other two external contact pads.
The current used is: from -0.01pA to 0.01pA.
The graphs are more or less straight lines. The strange thing is that at 0 current the voltage is different from zero (around 300 mV).
The idea is that there aren't ohmic contacts , because for ohmic contacts at 0 current the voltage drop should be zero too.
Anyway I don't understand why there is a voltage drop at 0 current.
In measuring resistance with the four-point-probe or van der Pauwmethods, we used 4 contacts (2 for current, 2 for voltage) to determine the sheet resistance of a layer while minimizing effects of contact resistance. However, in transistors and other electronic devices, the contacts are a necessary part of the device, and it is useful to determine the contact resistance so that we can have some idea of how it might affect device performance.We can measure the contact resistance using an extension of the resistance techniques employed earlier.Consider the simple
resistor geometry is shown
at right in cross section.
L
The measured total resistance consists of several components:
where Rm is the resistance due to the contact metal, RC is associated
with the metal/semiconductor interface, and Rsemi is the usual
semiconductor resistance.
The resistance of a single contact would be Rm + RC. However, in most
situations, the resistivity of the metal in the contact is so low that RC >>
Rm, and so Rm can be ignored.
the two probes for voltage measurement are in 2 contact pads distant 70micron and the other 2 probes for current injection are in other two external contact pads.
Dear Manlio Mignosa ,
welcome,
As you measure a material with very high resistance then the voltmeter may be of the type electrometer with vey high gain amplifiers. Such voltmeters may have to be zeroed before measurement. Which means that this voltage is generated in your voltmeter and you have to refer to the manual of your voltmeter and how you zero it.
The other cause may be due to interference from any nearby source.
When you measure such very impedances you have to shield your probe station to avoid any interference from surrounding sources.
Best wishes
It could be the open-circuit voltage generated by the photovoltaic effect, as suggested by Zekry. That depends on the measurement circuit. Is the I = 0 condition obtained by opening the current circuit -- or is it enforced by a power supply?
- Badges
- Science topic
- Similar topics
- Engineering
- Modeling