p-type Depletion Region n-type

CB VB $E_F$ $E_g$ E-field (n→p)

− − + +

− acceptor ions + donor ions

Key observations from diagram:

• The conduction band and valence band bend across the depletion region due to the internal electric field
• The Fermi level ($E_F$) is flat and continuous across the junction at equilibrium — essential thermal equilibrium condition
• Negative acceptor ions (p-side) and positive donor ions (n-side) create the internal E-field pointing from n to p
• The band bending creates an energy barrier that electrons must overcome to diffuse from n→p