# How do Zener diodes work?

I was going through some of the theory behind Zener diodes. I know what they're used to work at constant voltage, but I don't know how they work. Actually, I kind of get that too, I know that voltage is constant until breakdown occurs (avalanche breakdown), but I don't get why a minimum current is needed to maintain a constant voltage, which is what the textbooks say. Why is there a minimum? I thought any current below the breakdown voltage was constant. I don't see why the voltage would vary through the diodes if it's below a set amount of current, yet remain constant between voltages x-y?

Any help would be greatly appreciated, I can't wrap my head round exactly what's going on inside the little buggers.

P.S, is there more of an appropriate question for the electronics section? As I know electronics is a natural part of physics, and I heard this kinda stuff gets studied quite a lot in physics exams.

Below the breakdown voltage the diode does not behave as a perfect insulator, but has a small leakage current. This means the voltage across the diode is strongly current dependant. The minimum current, $I_{Z(mini)}$, is simply the current at which the breakdown is established and the voltage becomes (roughly) constant. If you're using the zener diode as a voltage regulator you need to maintain at least this minimum current to keep the voltage drop across the diode constant.