Zener – Explanation for the Shape of the Zener Avalanche Effect

avalanche-breakdownzener

The following diagram is a trace of a Zener diode in avalanche. I can understand the explanations behind shapes A – D, but what causes shape E?

A is the accumulating charge within the junction's capacitance, and thus follows the common exponential form. But no charge seems to accumulate immediately following breakdown (shape B).

And from my own experiment, this time with a 24V diode at 30V:-

My theory is the electrons are cascading so fast that they're exceeding the current flow through the 100k resistor, spurred on by impact ionisation. So no charge can build. The avalanche gradually stops between ~26.4V and ~28V, and only then does charge rebuild > 28V.

Is this correct?

Best Answer

The breakdown event involves a very fast pulse of current. Any circuit of nonzero size also has nonzero inductance. That voltage "spike" you're pointing to is the result of that current pulse interacting with that inductance.

$$V = L\frac{d i(t)}{d t}$$

Setup

In general, a setup like yours is able to detect muons.
The number of 25 firing pixels (we called them so) sounds reasonable, since muons don't produce many photons.
Your sensors are not ideal. A large number of pixels usually comes with a low capacity per pixel, i.e. low signal per firing pixel. Plus, the dark rate, i.e. the number of pixels firing spontaneously (That's what you see in figure 3b!) increases a lot, and the probability of two or more pixels firing at the same time increases, too. I would have used a devices with in the order of 1000 pixels, or even less.
By placing four arrays onto a small PCB, the manufacturer easily made a device with lots of pixels, but you shouldn't expect to get much spatial information of the trajectories from them. They are located too near to each other and will collect roughly the same amount light. This is especially true since the scintillator is quite diffuse for the produced light, and the light is reflected at the borders of the material. In addition, this makes the trigger system more complex.
Why are you using a stack of four scintillators? Typically, two are sufficient. If the green part is a thick iron plate, this yet could be used to detect pions, which generate large signals in the upper scintillators, convert to muons in the iron, and then generate low signals in the lower scintillators.

Electronics

What's very important for your system is to detect coincidences between all sensors. Each sensor will produce signals for muons from all directions, but you only want the signals of muons passing all scintillators from top to bottom.
Each sensor should give a trigger signal, which is then fed into a fast AND gate. This way, you get a trigger signal when all sensors saw something at the same time. The signals from the sensors should be short, otherwise you'll see coincidences where there are none. And don't forget cable lengths. You can even use different lengths to compensate for the time offset due to the time of flight of the muons.
To measure the amplitude, we used a charge-to-voltage transducer with variable gain and variable integration time, which also stretched the signal over time, making everything else less time critical. The signal was then fed through a sample-and-hold mechanism to "freeze" the voltage level a certain time after the trigger signal. It could then be measured with any cheap ADC.
If you want to measure precise amplitudes, keep in mind that your sensors are very sensitive to supply voltage (more gives higher signal, but also higher dark rate) and temperature (lower means higher signal and lower dark rate, one can increase voltage to increase signal further). Typically, you can use short light pulses (a few ns long) to measure discrete values like in figure 5 to calibrate your system.

Best Answer

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Setup

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