I'm working with chemiresistors, sourcing V and measuring I. For some of my sensors, I'm getting an IV curve that is linear, but does not pass through the origin. The plot shows a small positive current (+1uA) when V = 0. I know that this result means that my resistor is not ohmic. What else can be inferred from this information? Am I getting slight capacitance?
Of course, there are many possibilities (some of them have been mentioned above) and no one can answer precisely if we do not know exact device structure. However, please try to assume the following idea. If there is non-zero current for zero applied voltage, there should be another one source of the potential drop. In other words, there is local electric field caused by the nature of your device or measurement setup. The potential difference can be due to many reason such as photovoltaic effect (this was mentioned above already), polarization effect (spontaneous as well as double-layer or other), space-charge effect (some localized states or interfaces are charged and for zero voltage bias you see discharging effect with long life-time), and others.
Without knowing the device structure nor the exact IV response, it is difficult to comment on what could be causing the behaviour.
A great resource of information (attached) for characterising devices worth looking at is:
Dieter K. Schroder: : "SEMICONDUCTOR MATERIAL AND DEVICE CHARACTERIZATION".
EDIT: If your chemiresistor has a metal-semiconductor junction I would take a look at Section 3.5 (page 157) on Schottky barriers. I have included a screenshot of one of the examples of the behaviour you may be observing (based on the information you provided).
You have a perpetum mobile. Current without voltage. Sell it.
Your measurements must be wrong. Or the devise is a battery.
I'm using a Keithley 236 SMU. My composite is mounted on an interdigitated microelectrode. My fiber composite passes through the origin but the film does not. Both are made of same material and both curves are linear. However, the film composite IV is shifted above the origin. I've remeasured them multiple times.
Also, when I source + or - V only, the line hits the origin. Only when I source - to +, or vice versa, do I observe the shift above origin.
Couple of ideas:
Have you tried high impedance voltage measurement? (to measure the EMF)
Does the offset change with temperature? If yes, with how much? The rate of change could give a clue what process is behind it.
If you have light on your junctions another possibility is that one of the junctions is acting as a photocell and creating some photocurrent. If you have some light on the sample try it with the light off.
Douglas raises an important point- it can be surprising how significant the photovoltaic effect can be.
http://onlinelibrary.wiley.com/doi/10.1002/pssb.19660160242/abstract
Of course, there are many possibilities (some of them have been mentioned above) and no one can answer precisely if we do not know exact device structure. However, please try to assume the following idea. If there is non-zero current for zero applied voltage, there should be another one source of the potential drop. In other words, there is local electric field caused by the nature of your device or measurement setup. The potential difference can be due to many reason such as photovoltaic effect (this was mentioned above already), polarization effect (spontaneous as well as double-layer or other), space-charge effect (some localized states or interfaces are charged and for zero voltage bias you see discharging effect with long life-time), and others.
Your junction may be wok like a photocell and also check the offset specification of your test equipment.
I found the same thing when I dont pattern my organic materials on the electrodes. This will disappear when I pattern it. And I think this is well-known but I dont know why too. It will be great if anyone can answer...
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