Positron annihilation studies on the behaviour of vacancies in LaAlO 3/SrTiO 3 heterostructures

The formation and diffusion of vacancies are studied in LaAlO3/SrTiO3 heterostructures. Oxygen vacancies (V-OS) appear easily in the SrTiO3 substrate during LaAlO3 film growth at 700 degrees C and 10(-4) Pa oxygen pressure rather than at 10(-3)-10(-1) Pa, thus the latter two-dimensional electron gas should come from the polarity discontinuity at the (LaO)(+)/(TiO2)(0) interface. For SrTiO3-delta/LaAlO3/SrTiO3, high-density V-OS of the SrTiO3-delta film can pass through the LaAlO3 film and then diffuse to 1.7 mu m depth in the SrTiO3 substrate, suggesting that LaAlO3 has V-OS at its middle-deep energy levels within the band gap. Moreover, high-density V-OS may combine with a strontium/titanium vacancy (V-Sr/Ti) to form VSr/Ti-O complexes in the SrTiO3 substrate at 700 degrees C.