Refer to this graph http://www.reuk.co.uk/What-is-a-Zener-Diode.htm The zener diode First the reverse biased set up then the depletion layer become bigger and bigger because the anode of the battery will attract the electron in n-type , leaving a lot of holes there. For the cathode, it will supply a lot of electrons to the p-type, increasing the depletion layer. When the reverse voltage is continually supplied to the zener diode, a lot of energy will be given to the electrons in covalent bonds, then the electrons from covalent bond will break and jump from valence band to conduction band. This is what we called zener breakdown.( the electrons from the covalent bond is the minority charge carriers which resulting in more reverse current?) And the electrons are continually being supplied with energy ,(the minority charge carriers or electrons become stronger and stronger?) then they will continually move in the circuit and then knock the atoms around them , again a lot of electrons will be produced either from the covalent bond or the valence electron of the atoms. This is what we called avalanche breakdown. (then how about the depletion layer there? Still there or is being destroyed?) Then for one characteristic of zener diode ,the voltage is independent to the current. And from the graph we can see that when it is zener breakdown, there will be infinite current produced, because the graph show the current will go to infinity.(but how can the current go infinity since we have so limited atoms that make up the diode?) The zener diode as a voltage regulator can continue to supply constant voltage(is that mean the zener diode is able to keep voltage across it stable always?) and vary its own current to accommodate the circuit.(how the zener diode is able to vary the current just to suit the circuit? By controlling the minority charge carriers?) This is so far what I know all about the zener diode , please correct me and answer me. Thank you very much.