Anisotropic diffusion of hydrogen dopants in crystalline InAlZnO

Hydrogen incorporation strongly affects carrier density and reliability in oxide semiconductors, yet its behavior in the crystalline indium–aluminum–zinc oxide has not been fully established. Using first-principles calculations, stable hydrogen incorporation sites and their migration characteristics were systematically examined. Hydrogen preferentially occupies oxygen atoms coordinated by three zinc atoms, which remain stable against dissociation with barriers exceeding 0.5 eV. In contrast to the crystalline indium–gallium–zinc oxide, where gallium and zinc readily intermix, the crystalline indium–aluminum–zinc oxide contains a distinct planar aluminum–oxygen layer that acts as a vertical diffusion barrier. Penetration across this dense hexagonal layer requires hydroxyl rotation rather than conventional dissociation–migration, leading to substantially higher activation energies. The combination of site selectivity and anisotropic migration enables confinement of hydrogen dopants within a sub-unit cell thickness, providing a pathway to localized conductivity enhancement while maintaining the wide bandgap and low carrier density of the bulk material.