Existence of two-dimensional hole gas at the interface of Bi(Zn, Ti)O[formula omitted]/SrTiO[formula omitted] heterostructures: An ab-initio study

Abstract

We present first-principles calculations for a system consisting of a varying number of layers of the ferroelectric semiconductor Bi(Zn, Ti)O3 (BZT) on top of SrTiO3 (STO) substrate. To begin with, we assume that a TiO2 layer in STO is connected to a BiO layer in BZT. We show that atomic relaxation has a significant effect on the electronic properties of the heterostructure. In the absence of relaxation, due to the large polarization in BZT, a two-dimensional electron gas is formed at the interface when one unit cell of BZT is placed on top of STO. When relaxation is taken into account, the polarization in BZT is reduced in value and reversed in direction; in this case the insulator-to-metal transition occurs when the number of BZT unit cells reaches four, and a two-dimensional hole gas is formed at the interface. We also consider the case where an SrO layer in STO connects to a (Zn, Ti)O2 layer in BZT, and show that, when three unit cells of BZT are added on top of STO, a two-dimensional electron gas is formed near the interface.