Hydrogen adsorption and carrier generation in LaAlO3-SrTiO3 heterointerfaces: a first-principles study

Using the first-principles method, we investigate the hydrogen adsorption on the polar AlO(2) surface of LaAlO(3)-SrTiO(3) 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 LaAlO(3) thickness. The adsorbed H atom donates electrons to the conduction band of SrTiO(3), which results in the metallic conductivity of SrTiO(3). The charge transfer from H to SrTiO(3) significantly alters the electrostatic boundary condition and the Coulombic divergence inside LaAlO(3) completely disappears when one H atom is adsorbed every (2 × 1) surface unit cell. Our results also indicate that H(2) or H(2)O molecules exothermically dissociate and adsorb on the surface when the LaAlO(3) layer is thicker than certain critical values, suggesting that the H adsorption may play a role in the conducting properties of LaAlO(3)-SrTiO(3) heterostructures observed in experiment.