  We investigated the role of oxygen vacancy in n-type interface of LaAlO3
(LAO) overlayer on SrTiO3 (STO) (001) by carrying out density-functional-theory
calculations. Comparing the total energies of the configurations with one
vacancy in varying locations we found that oxygen vacancies favor to appear
first in LAO surface. These oxygen vacancies in the surface generate a
two-dimensional distribution of carriers at the interface, resulting in band
bending at the interface in STO side. Dependent on the concentration of oxygen
vacancies in LAO surface, the induced carrier charge at the interface partially
or completely compensates the polar electric field in LAO. Moreover, the
electronic properties of oxygen vacancies in STO are also presented. Every
oxygen vacancy in STO generates two electron carriers, but this carrier charge
has no effect on screening polar field in LAO. Band structures at the interface
dependent on the concentrations of oxygen vacancies are presented and compared
with experimental results.
