The oxygen vacancies in the LaAlO3 layer of the LaAlO3/SrTiO3 interface system*

Oxygen vacancies have been rarely studied in the top LaAlO₃ layer of the LaAlO₃/SrTiO₃ quasi-two-dimensional electron gas system. Here we found compelling evidences of oxygen vacancy formation in the top LaAlO3 layer using combined experiments of Layer by layer pulsed laser deposition growth, X-ray photoemission and X-ray diffraction. We found that the amount of oxygen vacancies in the LaAlO₃ layer is predominately determined by the deposition rate, instead of the commonly thought oxygen partial pressure. Moreover, sub-atmosphere pressure of oxygen post-annealing is necessary for completely removing the oxygen vacancies in the LaAlO₃ layer on top of the SrTiO₃ substrate. Our study shines new light on the physical mechanism supporting the formation of the quasi-two-dimensional electron gas.