11. MQW devices must be operated at high reverse bias fields to achieve good contrast ratios. 12. In this diode the voltage remains relatively constant ( independent of current ) when it is connected in reverse bias . 13. Under reverse bias , the diode ordinarily does not conduct ( save a small dark current or I s leakage ). 14. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. 15. In either formulation, r _ O varies with DC reverse bias V _ { CB }, as is observed in practice. 16. The small current that flows under high reverse bias is then the result of thermal generation of electron-hole pairs in the layer. 17. When this energy level is higher than that of the electrons, no tunnelling will occur, and the diode is in reverse bias . 18. The collector depletion region also increases under reverse bias , more than does that of the base, because the collector is less heavily doped. 19. This depletion region is much larger than in a PN diode, and almost constant-size, independent of the reverse bias applied to the diode. 20. There is also a recovery concern where the current will not decrease immediately when it is switched from forward bias to reverse bias .
