I have trouble understanding conductivity of a n-doped semiconductor in the band theory.
I know that donator atoms carry one excess electron that can enter the conduction band easily. If this happens, a fixed positive charge remains.
Assume that due to an applied voltage, the excess electrons in the conduction band are all removed from the semiconductor. How can the current continue to flow, how can new electrons enter the semiconductor or the conduction band?
Are the doping atoms "close enough" to each other so that excess electrons can move from doping atom to another?
I have less trouble understandung conductivity in a p-doped SC: an electron "fills up the missing bond", creating a fixed negative charge. Conduction occurs in the valence band by "passing the hole" from one Si atom to the next.