there are many types of diodes, so I'm going to attempt a very quick round up of the three main diodes that have interested me:
Silicone diode:
the silicone diode was covered before, it has a high reverse breakdown voltage (i.e would not conduct in reverse unless a large voltage was applied to it), it's activation energy is 0.7 volts (it will not forward conduct until this time.)
The way in which the diode goes from non-conduction to conduction is rather like a transistor, there is a curve that is centred around 0.7 volts
Germanium diode
The germanium diode is pretty similar to the silicone diode, however it is a lot older. it still has a high reverse breakdown voltage (though not as high as a silicone diode, but it's activation energy is lower at a mere 0.3 volts.
The conduction curve for the germanium diode is centreed around 0.3 volts
Zener Diode
the zener diode is a little weird, it's symbol is the same as a regular diode, except with the edition of a flare on either side of the bar in the symbol.
What makes a zener diode weird is it's breakdown voltage figures and behaviour
For a silicon diode, once the breakdown voltage for the component is reached that's it, the diode gives up, it conducts in forward connection and reverse connection, it's more like a piece of wire than a diode, or maybe a resistor. but certainly not a diode.
A zener diode has a very specific breakdown voltage, (of say 9 volts) and it recovers from this too! so that it only conducts in reverse when the voltage applied to the positive side of the component is above the breakdown voltage.
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