First-principles studies of polar perovskite KTaO surfaces: structural reconstruction, charge compensation, and stability diagram.

Polar perovskite oxides are of considerable interest for developing advanced functional materials with exceptional electronic properties for their unique polar characters. A cleavage of polar perovskite oxides along the charged layers leads to an electrostatic instability on the cleaved surfaces, and a charge compensation is required to stabilize these surfaces. In this work, we have systemically studied 25 types of surface models of polar KTaO3 perovskite oxide, including (001), (110), and (111) surfaces with various types of surface terminations, using first-principles electronic structure calculations.

High-Throughput Design of Two-Dimensional Electron Gas Systems Based on Polar/Nonpolar Perovskite Oxide Heterostructures.

The two-dimensional electron gas (2DEG) formed at the interface between two insulating oxides such as LaAlO and SrTiO (STO) is of fundamental and practical interest because of its novel interfacial conductivity and its promising applications in next-generation nanoelectronic devices. Here we show that a group of combinatorial descriptors that characterize the polar character, lattice mismatch, band gap, and the band alignment between the perovskite-oxide-based band insulators and the STO substrate, can be introduced to realize a high-throughput (HT) design of SrTiO-based 2DEG systems from perovskite oxide quantum database. Equipped with these combinatorial descriptors, we have carried out a HT screening of all the polar perovskite compounds, uncovering 42 compounds of potential interests.

Creating Two-Dimensional Electron Gas in Polar/Polar Perovskite Oxide Heterostructures: First-Principles Characterization of LaAlO3/A(+)B(5+)O3.

By using first-principles electronic structure calculations, we explored the possibility of producing two-dimensional electron gas (2DEG) at the polar/polar (LaO)(+)/(BO2)(+) interface in the LaAlO3/A(+)B(5+)O3 (A = Na and K, B = Nb and Ta) heterostructures (HS). Unlike the prototype polar/nonpolar LaAlO3/SrTiO3 HS system where there exists a least film thickness of four LaAlO3 unit cells to have an insulator-to-metal transition, we found that the polar/polar LaAlO3/A(+)B(5+)O3 HS systems are intrinsically conducting at their interfaces without an insulator-to-metal transition. The interfacial charge carrier densities of these polar/polar HS systems are on the order of 10(14) cm(-2), much larger than that of the LaAlO3/SrTiO3 system.

Polarization effects on the interfacial conductivity in LaAlO3/SrTiO3 heterostructures: a first-principles study.

We studied the influence of uniaxial [100] strain (-1% to +1%) on the electron transport properties of a two-dimensional electron gas (2DEG) at the n-type interface of the LaAlO3/SrTiO3(LAO/STO) heterostructure (HS)-based slab system from the perspective of polarization effects via first-principles density functional theory calculations. We first analyzed the unstrained system, and found that the induced polarization toward the vacuum in the LAO film leads to a small charge carrier density on the order of 10(13) cm(-2) (less than the theoretical value of 3.3 × 10(14) cm(-2) from the superlattice-model-based polar catastrophe mechanism), which is in excellent agreement with the experimental values of oxygen-annealed LAO/STO HS samples.

Energetic stability, oxidation states, and electronic structure of Bi-doped NaTaO3: a first-principles hybrid functional study.

We studied the defect formation energies, oxidation states of the dopants, and electronic structures of Bi-doped NaTaO3 using first-principles hybrid density functional theory calculations. Three possible structural models, including Bi-doped NaTaO3 with Bi at the Na site (Bi@Na), with Bi at the Ta site (Bi@Ta), and with Bi at both Na and Ta sites [Bi@(Na,Ta)], are constructed. Our results show that the preferred doping sites of Bi are strongly related to the preparation conditions of NaTaO3.

Nb and Ta layer doping effects on the interfacial energetics and electronic properties of LaAlO3/SrTiO3 heterostructure: first-principles analysis.

The two-dimensional electron gas (2DEG) formed at the n-type (LaO)(+1)/(TiO2)(0) interface in the polar/nonpolar LaAlO3/SrTiO3 (LAO/STO) heterostructure (HS) has emerged as a prominent research area because of its great potential for nanoelectronic applications. Due to its practical implementation in devices, desired physical properties such as high charge carrier density and mobility are vital. In this respect, 4d and 5d transition metal doping near the interfacial region is expected to tailor electronic properties of the LAO/STO HS system effectively.

Interface Energetics and Charge Carrier Density Amplification by Sn-Doping in LaAlO3/SrTiO3 Heterostructure.

Tailoring the two-dimensional electron gas (2DEG) at the n-type (TiO2)(0)/(LaO)(+1) interface between the polar LaAlO3 (LAO) and nonpolar SrTiO3 (STO) insulators can potentially provide desired functionalities for next-generation low-dimensional nanoelectronic devices. Here, we propose a new approach to tune the electronic and magnetic properties in the n-type LAO/STO heterostructure (HS) system via electron doping. In this work, we modeled four types of layer doped LAO/STO HS systems with Sn dopants at different cation sites and studied their electronic structures and interface energetics by using first-principles electronic structure calculations.