Oxygen Vacancy Effects of Two-Dimensional Electron Gas in SrTiO3/KNbO3 Hetero Structure

Abstract

The discovery of a two-dimensional electron gas (2DEG) in LaAlO3 (LAO)/SrTiO3 (STO) heterostructure has stimulated intense research activity. We suggest a new structure model based on KNbO3 (KNO) material. The KNO thin films were grown on TiO2-terminated STO substrates as a p-type structure (NbO2/KO/TiO2) to form a two-dimensional hole gas (2DHG). The STO thin films were grown on KNO/TiO2-terminated STO substrates as an n-type structure to form a 2DEG. Oxygen pressure during the deposition of the KNO and STO thin films was changed so as to determine the effect of oxygen vacancies on 2DEGs. Our results showed conducting behavior in the n-type structure and insulating properties in the p-type structure. When both the KNO and STO thin films were deposited on a TiO2-terminated STO substrate at a low oxygen pressure, the conductivity was found to be higher than that at higher oxygen pressures. Furthermore, the heterostructure formed at various oxygen pressures resulted in structures with different current values. An STO/KNO heterostructure was also grown on the STO substrate, without using the buffered oxide etchant (BOE) treatment, so as to confirm the effects of the polar catastrophe mechanism. An STO/KNO heterostructure grown on an STO substrate without BOE treatment did not exhibit conductivity. Therefore, we expect that the mechanics of 2DEGs in the STO/KNO heterostructures are governed by the oxygen vacancy mechanism and the polar catastrophe mechanism.