When a p−n junction is formed, the hole concentration is more in P side as compared to N side and electron concentration is more in N side as compared to P side. So, diffusion of charge carrier from lower to higher concentration continues and an equilibrium is established forming a potential barrier. The barrier produces an electric field.
Drift of charge carriers due to the force exerted on charge carriers by the electric field. So, when a potential barrier is established, it opposes the diffusion of majority charge carriers from one region to other, but supports the drift of minority carrier.