sentences:  Breakdown voltage for commonly available Zener diodes can vary widely from 1.2 V to 200 V.
  
  For diodes that are lightly doped the breakdown is dominated by the avalanche effect rather than the Zener effect.Consequently, the breakdown voltage is higher (over 5.6 V) for these devices.The emitter-base junction of a bipolar NPN transistor behaves as a Zener diode, with breakdown voltage at about 6.8 V for common bipolar processes and about 10 V for lightly doped base regions in BiCMOS processes.