= Band offset
{title2=$\Delta E_c,\Delta E_v$}
A <band offset> is an interface discontinuity in a <conduction band> or <valence band> edge.<Nobel Lecture: Quasielectric fields and band offsets: teaching electrons new tricks by Herbert Kroemer>[§VIII, Fig. 12, pp. 790–791]{ref}
For a chosen two-material example, let the central material A have $E_{c,A}=1$ and $E_{v,A}=0$, and the surrounding material B have $E_{c,B}=1.6$ and $E_{v,B}=-0.4$, in stipulated <energy> units. Define positive confinement barriers by $\Delta E_c=E_{c,B}-E_{c,A}$ and $\Delta E_v=E_{v,A}-E_{v,B}$. Then $\Delta E_c=0.6$, $\Delta E_v=0.4$, and the <band gaps> obey
$$
E_{g,B}-E_{g,A}=\Delta E_c+\Delta E_v=1.
$$
This identity determines the sum of the <band offsets>; a <band gap> difference alone cannot determine their partition. The chosen numbers illustrate the definition and do not specify a measured material pair.
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