Influence of charge compensation mechanisms on the sheet electron density at conducting LaAlO 3 /SrTiO 3 -interfaces

The equilibrium conductance of LaAlO 3 /SrTiO 3 (LAO/STO)-heterointerfaces was investigated at high temperatures (950K-1100K) as a function of ambient oxygen partial pressure (pO 2 ). Metallic LAO/STO-interfaces were obtained for LAO grown on STO single crystals as well as on STO-buffered (La,Sr)(Al,Ta)O 3 substrates. For both structures, the high temperature sheet carrier density n S of the LAO/STO-interface saturates at a value of about 1×10 14 cm −2 for reducing conditions, which indicates the presence of interfacial donor states. A significant decrease of n S is observed at high oxygen partial pressures. According to the defect chemistry model of donor-doped STO, this behavior for oxidizing conditions can be attributed to the formation of Sr-vacancies as charge compensating defects.