Nanomaterials - 18

Abstract

Transparent oxide semiconductors (TOSs) are attracting considerable attention as thin-film transistor channels for driving flat panel displays and transistors for high-power applications with high mobility. The representative example is amorphous indium gallium zinc oxide (IGZO) for the backplane to drive flat panel displays. However, the conduction type of TOS is practically restricted to the n-type, which is a major obstacle to extending the device applications based on the p–n junction such as LED or CMOS. The difficulty in p-type conduction is common in wide-gap semiconductors. Anionic p orbitals primarily constituting the valence band maximum (VBM) are localized owing to the highly electronegative nature of the anion.[1, 2] Thus, a novel approach to modifying the VBM is pivotal to realizing p-type conduction.(Fig. 1) Here, we report a new approach to VBM modulation through the covalent interaction with filled cationic p orbitals. LaN is taken as an example. (Fig. 2) 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 ionization potential and enhances the dispersion of VBM, leading to a direct-type bandgap. Cationic p states (La 5p6) located energetically near the VB and linear coordination of La–N chains present in rocksalt-type crystal structure are keys to making the N p–La p covalent interaction strong.