What is a typical diode's ideality factor?

Question

Some background, for anyone unfamiliar: The Shockley diode equation is

$$ I_D = I_S·\left(e^{\frac{V_D}{n·V_T}}-1\right) $$

with the quantity \$n\$ called the ideality factor, a number between 1 and 2. Ideal diodes have an ideality factor of 1, while real diodes do not. (And, to my understanding, the ideality factor of real diodes can depend strongly on temperature and diode current.)

My question is this: What is a typical ideality factor for commercially-available pn diodes at room temperature? In what range can one expect the ideality factor to be? Will it be different for Schottky diodes?

The impression I got from my semiconductor devices class is that it's close to 2 for low currents, shifts nearer to 1 for moderate currents, and goes back to 2 at very high currents; is this correct? Are there more precise numbers available anywhere?

Answer 1

I am currently taking a semiconductor class and we recently did an experiment to measure the ideality factor for two different diodes, one of germanium and one of silicon composition. The experiment found the silicon diode to have an ideality factor of 1 and the germanium to have a factor of 1.4. According to my professor the ideality factor is indicative of the type of charge carrier recombination that is occurring inside of the diode based on the following chart.

Recombination Type	n	Description
SRH, band to band (low level injection)	1	Recombination limited by minority carrier.
SRH, band to band (high level injection)	2	Recombination limited by both carrier types.
Auger	2/3	Two majority and one minority carriers required for recombination.
Depletion region (junction)	2	Two carriers limit recombination

In order to calculate n, I measured and graphed the I-V (V being the voltage across the diode not the applied voltage) characteristics of the diodes and found the slope as such:

Then knowing this relationship where e is the charge of an electron, T is temperature and K is the Boltzman constant and \$I_{0}\$ is the inverse saturation current

$$ \ln I = \ln I_{0} + \frac{1}{n} \left( \frac{eV}{kT} \right). $$

I find the slope of the graph to be

$$ m = \frac{1}{n} \frac{e}{kT}. $$

Solving for n yields a 1.

I think that answers 3 out of 5 of your questions.

I hope all of that helped!

Answer 2

https://www.youtube.com/watch?v=BC1E13CKf8g

You can watch this video. An ideal diode has the ideality factor of 0. Forward bias, the current --> infinity. Reverse bias, the current --> 0. This diode does not exist in real life. And due to the recombination property of the Si and Ge, all the diode made by these two materials have the ideality factor between 1 and 2. The diode having ideality factor <1 does not exist either.