I have IV characteristic of a diode. How to plot ideality factor versus applied voltage? Saturation current (Isat) is calculated from the diode equation? I tried plotting ideality factor vs voltage by using the equations of diode, but ended up in linear graph, which I guess should be a bell shaped (gaussian)?
See this: G. a. H. Wetzelaer, M. Kuik, M. Lenes, and P.W.M. Blom, Appl. Phys. Lett. 99, 153506 (2011).
To measure ideality factor; leakage current might be quite low at low voltages in the diffusion limit!
Ideality factor is the measure how close the IV characteristics is to the one of an ideal diode - e.g described by equation presented here:
http://www.pveducation.org/pvcdrom/solar-cell-operation/ideality-factor
therefore you cannot get the ideality factor vs voltage.
What one may do is to calculate ideality factor, then generate "the most fitting"" IV curve for above equation and present a function:
q(V) = sqrt(I(V)-I_ideal(V))^2
this will give you a measure how close the measured diode is to an ideal one at particular voltage
You may consider the approach presented in V. Mikhelashvili et al., "Extraction of Schottky diode parameters with a bias dependent barrier height" Solid State Electronics 45(1):143-148, Jan 2001. And you are right, the curve is bell shaped.
Take look on Shottky model
I(V)=Is*(exp(V/(N*kT/e))-1).
Take two points (V1,I1) and (V2,I2) near Imax.
Ln(I2/I1)~=(V2-V1)/(N*kT/e).
If I2=2.7*I1 then Ln(I2/I1)=1, and N=(V2-V1)/(kT/e) is ideality factor.
For room temperature kT/e=25mV
It's always interesting to measure the dark I-V, then plot the differential resistance vs voltage. For a good diode, you'll get a high-impedance plateau at lower voltages depending on the residual illumination, the shunting in your device, and the quality of your measuring instrument. Then at increasing voltages you'll get a straight line on a log scale up to a point at which the series resistance's contribution makes the straight line deviate. You can extract the n factor from the slope of the log plot in the straight regions and/or plot n vs V from the local slope, by taking care of scaling appropriately with the proper constants from the diode equation...
Please see the reference:
Kirchartz, T., Deledalle, F., Tuladhar, P. S., Durrant, J. R., & Nelson, J. (2013). On the differences between dark and light ideality factor in polymer: fullerene solar cells. The Journal of Physical Chemistry Letters, 4(14), 2371-2376.
Wetzelaer, G. A. H., Kuik, M., Lenes, M., & Blom, P. W. M. (2011). Origin of the dark-current ideality factor in polymer: fullerene bulk heterojunction solar cells. Applied Physics Letters, 99(15), 153506.
- Badges
- Science topic