Why Is the Bandgap of GaP Indirect While That of GaAs and GaN Are Direct?

Many III–V semiconductors possess direct bandgaps and are thus widely applied in optoelectronics. Although GaN (either in wurtzite phase or zinc blende phase), GaAs, and GaSb are well‐known direct‐gap semiconductors, GaP exhibits an indirect bandgap nevertheless. In this work, the generic rule of energy gaps in GaN, GaP, and GaAs of the zinc blende phase is analyzed, and the trends of gap variation are studied concerning the lattice constant and anion electronegativity. It turns out that GaP actually manifests a normal behavior, the reason why GaN surprisingly has a direct gap is analyzed through examining and perturbing its valence band as well as conduction band (CB). The CB electron shows a non‐negligible probability to emerge near the N cores. The attractive nucleus potential pulls down the CB more strongly at Γ, which is in principle further supported through an analysis of the Kronig–Penney model. The difference between GaP and GaN in this respect is also analyzed in detail.