Valence Band Modulation Using Cationic Filled p Orbitals toward p-Type Conduction

p-Type conduction is difficult in wide-gap compound semiconductors, such as transparent oxides. Anionic p orbitals primarily constituting the valence band maximum (VBM) are localized owing to their highly electronegative nature, which gives rise to a large ionization potential (Ip), leading to a difficulty in hole doping into the VBM. Here, we report a new approach to VBM modulation through the covalent interaction with filled cationic p orbitals. LaN is taken as an example. Pushing the anionic valence band (VB) to VBM by σ interaction in N–La chains between the N 2p VB and the filled La p orbitals decreases Ip and enhances the dispersion of VBM, leading to a direct-type band gap. Cationic p states (La 5p6) located energetically near the VB and linear coordination of La–N chains present in rock-salt-type crystal structures are keys to making the N p–La p covalent interaction strong.