= Electron-hole symmetry
{title2=$E_c(\mathbf k)=-E_v(\mathbf k)$}
Symmetry of the excitation spectrum under exchange of <conduction band> <electrons> and <valence band> <holes>, after choosing a central zero of <energy>. In a two-band model with equal <effective masses> and equal <degeneracy factors>, <charge neutrality> in an <intrinsic semiconductor> fixes the <chemical potential> at that central <energy>. Indeed the <Fermi-Dirac distribution> obeys $1-f(-E;\mu=0)=f(E;\mu=0)$, so excitation populations are equal at every positive <energy>.
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