Rules for band diagrams
• Valence states are filled with electrons, conduction bands
are partially or completely empty.
• Outer electrons from donor or acceptor dopants usually
exist in isolated states within the bandgap (near the
conduction or valence bands, respectively).
• Electrons fall down in energy, holes ‘fall’ up.
• For joined materials, the Fermi level is always flat.
• For joined materials, the band edges shift and/or bend any
way that is necessary to accommodate a flat Fermi level.
• Applied biases shift the Fermi level, and the conduction
and valence bands, on the side with the bias.
• A positive applied bias moves the bands down where it
is applied; a negative bias moves them up.
• Again, band bending occurs near the interfaces to
accommodate applied biases.