Why there is no movement of charge carrier inside PN junction diode once barrier is formed ?

Lets  answer to this question but before , we should understand some basics of PN junction diode.

PN junction diode is formed by sandwich of P type material with the N type material.

Now once these materials are combined , there will be diffusion.

Diffusion can be understood this way , as the holes are the  majority concentration in P side ,  they will  try to move towards N region so that it can balance the concentration. Same thing happen with the electrons available in N side.

Now once , some of the charge carrier moved from N to P and some from P to N.

There will be a barrier and that region is also called as depletion region .

If we look at the above fig , what we can see here is , because of the barrier , there will be barrier voltage ( for Ge it is 0.3 and for Si it is 0.7 V) . Also there is electric field which is pointing from N to P .

 we also know that E field always point in direction in which holes are moving or in a direction opposite of electron movement.

Because of this Electric field , holes are unable to move towards the N region and same is true for electrons in N side.

Now once we bias the diode , we on general say that applied voltage should be greater than 0.7 volts for Si diode , this is because, so that E ( applied ) should be able to overcome the E ( field because of barrier)  and then our diode will conduct.