Hydrogen adsorption and carrier generation in LaAlO₃-SrTiO ₃ heterointerfaces: A first-principles study

Using the first-principles method, we investigate the hydrogen adsorption on the polar AlO₂ surface of LaAlO₃-SrTiO₃ heterostructures with an n-type interface. It is found that the H atom is most stable when bound at the surface O atom. The adsorption energy for a given H density is lowered (i.e., stronger binding) with increasing LaAlO₃ thickness. The adsorbed H atom donates electrons to the conduction band of SrTiO₃, which results in the metallic conductivity of SrTiO ₃. The charge transfer from H to SrTiO₃ significantly alters the electrostatic boundary condition and the Coulombic divergence inside LaAlO₃ completely disappears when one H atom is adsorbed every (2 x 1) surface unit cell. Our results also indicate that H₂ or H ₂O molecules exothermically dissociate and adsorb on the surface when the LaAlO₃ layer is thicker than certain critical values, suggesting that the H adsorption may play a role in the conducting properties of LaAlO₃-SrTiO₃ heterostructures observed in experiment.