 Heavy-hole and light-hole bands

Near the zone centre of many cubic semiconductors, the upper valence bands have different curvatures and hence different band effective masses. In the isotropic approximation, the $j=3/2$ states with angular-momentum projection magnitude $3/2$ along the propagation direction form the heavy-hole branch; projection magnitude $1/2$ gives the light-hole branch. A flatter downward electron dispersion corresponds to a larger positive electron hole effective mass. Crystal anisotropy, strain and confinement can mix these branches, so the labels do not imply direction-independent exact masses.