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

Intrinsic defects are crucial to the electronic and magnetic properties the SrTiO3/LaAlO3 (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 TiO2 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 internal electric field, leading to a wider band gap in the system with both n- and p-type interfaces.