Determining the saturation current

1. Jan 30, 2012

sandy.bridge

Hello all, I have a GaAs LED, and I want to determine the saturation current. I have numerous points from 0.5V-2.9V, with currents of 0.1uA-50mA. I have plotted it on semi-log paper, however, the only linear segment is from 1uA-5000uA, and then it begins to curve downwards. I used the linear segment to determine the saturation current, and the value of "n", however, they hardly describe the diode for anything else beyond this linear segment... Have I done something improper for determining these values?

Note: if I do a scatter plot in excel of all my points, the linear segment is rather from 5mA-50mA

Last edited: Jan 30, 2012
2. Jan 30, 2012

sandy.bridge

Whoops, somehow the axes were messed. Check the attached:
Also attached is the semi-log graph

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Last edited: Jan 30, 2012
3. Feb 26, 2012

StrykerTECH

The reverse saturation current (Is) for a diode is typically modeled as I = Is * (e^(V/(nVt)) - 1). This model is applicable to LEDs only for very low forward currents. For forward currents above a few mA, the ohmic losses in the LED must be included to accurately model the forward voltage. You are going to need to calculate the LED series resistance based on the measurements you’ve collected.

I’ve attached an application note that shows a procedure for calculating the reverse saturation current, n, and series resistance of an LED using the forward current measurements you’ve already made.

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