Show the direction of the electric field that arises in a $p-n$ junction.

(N/A) When a $p-n$ junction is formed,electrons diffuse from the $n$-region to the $p$-region,and holes diffuse from the $p$-region to the $n$-region due to the concentration gradient.
This diffusion leaves behind ionized donor atoms (positive charges) in the $n$-region and ionized acceptor atoms (negative charges) in the $p$-region near the junction.
These immobile charges create an electric field directed from the $n$-region (positive side) to the $p$-region (negative side).
Therefore,the direction of the electric field in the depletion region of a $p-n$ junction is from the $n$-side to the $p$-side.