Zener effect - how does the probability of tunnelling increase under an increasing potential barrier?

Question

From Wikipedia (the basis of my lectures):

Under a high reverse-bias voltage, the p-n junction's depletion region widens which leads to a high-strength electric field across the junction.
Sufficiently strong electric fields enable tunneling of electrons across the depletion region of a semiconductor, leading to numerous free charge carriers.

I'd expect the widening of the depletion zone and the increasing potential barrier to reduce the chance of tunnelling, not to increase it. How is the opposite possible?

lnmaurer · Accepted Answer

I don't think that the Wikipedia article is correct. The widening doesn't cause tunneling; the shifting of the bands does. Maybe this figure helps (also from wikipedia):

(Zener tunneling is the right-most subfigure.)
In fact, I've never heard of this widening. I guess that it could happen, but I've never seen it in any models of Zener tunneling, so I don't think widening is important if it does happen.
I should add that the hyperphysics link conflates the Zener effect and avalanche breakdown. The two are different things altho they have a similar effect and can happen in the same device. (In fact, many "zener" diodes that you can buy at electronics suppliers don't really rely on Zener tunneling; they use avalanche breakdown.) Zener tunneling is in fact quantum tunneling.

Zener effect - how does the probability of tunnelling increase under an increasing potential barrier?

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