Stabilities of the Intrinsic Defects on SrTiO3 Surface and SrTiO3/LaAlO3 Interface

Intrinsic defects are crucial to the electronic and magnetic properties in the SrTiO 3 /LaAlO 3 (STO/LAO) system. With the first-principles simulation, we construct a formation energy phase diagram of different intrinsic defects on STO surfaces. The three most stable surface defects are Al-substitution of Ti, La-substitution of Sr, and the oxygen vacancy at TiO 2 surface. On STO, multiple defects are possible. When these defective surfaces form interfaces with LAO, the Al substitution of Ti atom is highly favored energetically. Defects of this type can change the n-type interface into p-type. The polar STO/LAO interface is found to effectively compensate the internal electric field, leading to a wider band gap in the system with both n- and p-type interfaces.