Question

How is there a -0.7V charge gap in a diode?

Answer 1

Because when reversed biased.. the band gap increases to its maximum size… there is no conduction possible…Now it will require some energy to break this band gap and allow conduction through this insulator, which is basically the energy gap of diode…. Look it this way, if diode is forward biased then there is no restriction to electrons.. so we cannot determine energy gap… so we have to reverse bias it

Answer 2

when a diode is reverse biased it act as a open switch due to band gap,this band gap is different for every diode depending upon the doping,so in reverse bias if the diode breaks down in less time then the band gap is small and if the band gap is large it doesn’t breaks for comparatively large time.

Zener diode is an example where it is reverse biased for current stability