# Diode emission coefficient and saturation current

I have created a Zener diode model in LTSpice, and now I am trying to simulate it with different values of the saturation current (IS), emission coefficient (N) and breakdown voltage (BV) using Spice.
These terms are not entirely clear to me, so analyzing the results of my simulations would be problematic. This is my understanding of the above in layman's terms:

Saturation current - This is the maximum reverse current caused by the combination of the minority particles in the p and n junctions, beyond which the zener diode enters breakdown voltage and this current exceeds rapidly, likely to damage the diode.

Emission coefficient - This concept is not clear to me. From what I read online, it is a value between 1 and 2. Closer to 1 means greater forward bias. But how do I apply this to my Zener diode simulations?

Breakdown voltage - The voltage which is greater than the barrier potential, beyond which the reverse current is not longer negligible and increases greatly.

I would appreciate if the accuracy of my understanding of the terms could be confirmed. Also, how do I put all this together to analyze and conclude my results of varying IS, BV and N?

• The emission coefficient is a model parameter and there are actually several of them. But I think you are talking about the forward biased one in the Ebers-Moll model. In a small signal BJT, it's n=1 mostly. In diodes, it's often n=1.7 to n=3 (sometimes.) There is a thermal voltage (kT/q) that is modified by n to be (nkT/q), instead. It's tweaked to help fit the idealized model to observed behavior. – jonk Aug 13 '16 at 18:21
• Not sure if I fully understand your comment. How does this affect the I-V characteristic graph of the diode? – abruzzi26 Aug 13 '16 at 21:25
• I wasn't trying to explain everything. If I were, I'd write an answer. I just wanted to dash off a possibly helpful note. The thermal voltage concept either means something to you or it doesn't. If it does, you might understand why a model parameter that fusses with that value may be needed. If not, it's beyond my interest to answer for now. – jonk Aug 13 '16 at 21:33