Hydrogen adsorption on the ZnO (1100) surface: Ab initio hybrid density functional linear combination of atomic orbitals calculations

Hydrogen atoms unavoidably presented in ZnO samples or thin films during their synthesis considerably affect electrical conductivity. Results of first principles hybrid functional linear combination of atomic orbitals calculations are discussed for hydrogen atoms incorporated in bulk or adsorbed upon non-polar ZnO (1100) surfaces. The energy of H incorporation, atomic relaxation, electronic density redistribution and modification of the electronic structure are compared for both surface adsorption and bulk absorption. It is shown that hydrogen forms a strong bonding with the surface O ions (E_ads = 2.7 eV) whereas its incorporation into bulk is energetically quite unfavorable. Hydrogen adsorption reduces the surface energy. Surface hydrogen atoms are very shallow donors, thus contributing to the electronic conductivity and ZnO metallization.