(There is a duplicated which wasn't that helpful.)
(My physics knowledge is highschool)
When the diode is in reverse bias,
There is a depletion region and there is no free electrons nor hole around the pn junction.
So it is totally understandable that there is no current from n-type to p-type.
But, why there is no current from p to n? The energy level of valance band of p-type is higher than n-type conduction band.
The red arrow is what I'm saying. The valence electron move to n-type semiconductor and become a free electron. Why is this not happening? Does valance electron can't move regardless of its higher energy level?
Does the valence electron first need to go up to p-type's conduction band to move to n-type conduction band?
And there is no enough energy to go up to p-type's conduction band even though energy level of p-type's valence band is higher than that of conduction band of n-type.
Is this the reason why there is no current from p to n?