Zeners look like...
Well, at least the avalanche effect, taken for a simple 24V Chekhov circuit inside our Dangerous Box:-
Strong Zener Avalanche effect at 100 µs/div.
Notice the peak to peak voltage which is natural and unamplified. And zoomed in horizontally 500 times:-
Strong Zener Avalanche effect at 200 ns/div.
These oscilloscope images closely match those from other published sources, such as a SenSys 2016 presentation and Krieger 2017.
Labelled parts of Zener Avalanche breakdown.
Notice here the magnitude of Vpp. It took nearly 30 minutes to catch this large 3.48 V peak as they’re rare. Also notice the Avalanche drop rate (slew). It’s approximately -80 MV/s. Wow, that’s fast! It’s almost a pure short. The slight bend of the charge curve is characteristic of exponentially reducing charge accumulation within a capacitance (with respect to time $t$) as:-
$$ V = V_o \big(1-e^{-t/RC} \big) $$
Capacitance $C$ arises from the Zener’s PN junction (approx. 150 pF) and the gate of the Dangerous Box’s MOSFET 2N7000 voltage follower (approx. 60 pF).