Formation and Tuning of 2D Electron Gas in Perovskite Heterostructures

Abstract

Oxide interfaces provide very intriguing phenomena, in particular a 2D electron gas (2DEG) emerging between robustly insulating perovskites. The 2DEG was detected in 2004 beneath polar LaAlO 3 (LAO) epitaxially grown on TiO 2terminated SrTiO 3 (001) (STO). Herein, recent first-principles studies of 2DEGs are reviewed. Using a Green function method, the family of the polar/nonpolar (001) interfaces: LAO/STO, LaFeO 3 /STO, and STO/KTaO 3 is computed. In the context of 2DEG, one of two insulating perovskites, at least, must be polar. The effect of a polar/polar interface is modeled for LAO/KTaO 3 (001) and also for the ( 110) and ( 111) interfaces of LAO/STO. Starting from the defectless superlattice with its two differently terminated interfaces, we demonstrate that the 2DEG and 2D hole gas appear there, respectively, due to the presence of excessive electrons or holes. 2DEG is evaluated by its layer-resolved density profile along [001], as well as the Fermi surface cross sections and effective masses, which are directly related to the transport properties. The effects of intermixed cations, their vacancies, and oxygen vacancies at each interface of LAO/STO are calculated. Finally, we show how to tune reversibly the 2DEG by changing the electronic balance at the LAO surface that mimics the effect of ionic liquid gating.

Tuning two-dimensional electron and hole gases at LaInO3/BaSnO3 interfaces by polar distortions, termination, and thickness

“…We also highlight the importance of the well-confined 2DHG hosted by O-p states in view of p-type conductivity. We note that in SrTiO 3 /LaAlO 3 /SrTiO 3 , another heterostructures [36] formed by a polar and a nonpolar material, only recently the presence of a 2DHG has been confirmed experimentally [37]. The coexistence of high-density well-confined electron and hole gases within one system as shown here, appears as a promising platform for exploring also intriguing phenomena such as long-lifetime bilayer excitons [38] or Bose-Einstein condensation [39].…”

“…Thereby, n-type (LaO/SnO 2 ) and p-type (InO 2 /BaO) building blocks are periodically replicated in the out-of-plane direction (z ). In this case, the system is stoichiometric and ideally suited for investigating the electronic reconstruction due to the polar discontinuity [15,36]. The BaSnO 3 block has a thickness of 10 unit cells which is enough to minimize the interaction with its replica [32], and the LaInO 3 block has a thickness of 12 pseudocubic unit cells.…”

Controlling Memristance and Negative Differential Resistance in Point‐Contacted Metal–Oxides–Metal Heterojunctions: Role of Oxygen Vacancy Electromigration and Electron Hopping

“…2 d electron gas (2DEG) is formed at oxides interface of LaAlO 3 /SrTiO 3 (111). [34][35][36] Atomic force microscope image (inset of Figure 1a) of LaAlO 3 /SrTiO 3 (111) heterostructure shows a smooth sample surface with a roughness of %0.3 nm Afterwards, 300 nm thick Pt electrodes were grown on LaAlO 3 /SrTiO 3 (111) surface by magnetron sputtering in Ar atmosphere using shadow masks, with sputtering power of 50 W. During the process of Pt growth and post-annealing, ohmic contact is formed between Pt electrodes and 2DEG at the oxides interface, as shown in Figure S1, Supporting Information. Point contact was made between the tungsten probe tip and perovskite oxides heterostructures by connecting the tungsten probe on LaAlO 3 /SrTiO 3 (111) surface.…”

Physical insights into the Au growth on the surface of a LaAlO3/SrTiO3 heterointerface

“…10 Several factors can affect the electronic conducting properties of the LAO/STO system: (1) oxygen vacancies, created during the fabrication process, 11 generate donor levels located near the conduction band of STO, 12 thereby changing the 2DEG state in the interface. (2) Pressure affects the existence and stability of two-dimensional electron gas. 13 The compression pressure induces ferroelectric polarization in the STO substrate, thereby altering the 2-dimensional electron gas by reversing the polarization direction of the STO substrate due to charge passivation and band gap alignment.…”