High Mobility Two-Dimensional Electron Gas at the BaSnO₃/SrNbO₃ Interface

Abstract

Oxide two-dimensional electron gases (2DEGs) promise high charge carrier concentrations and low-loss electronic transport in semiconductors such as BaSnO 3 (BSO). ACBN0 computations for BSO/SrNbO 3 (SNO) interfaces show Nb-4d electron injection into extended Sn-5s electronic states. The conduction band minimum consists of Sn-5s states ∼1.2 eV below the Fermi level for intermediate thickness 6-unit cell BSO/6unit cell SNO superlattices, corresponding to an electron density in BSO of ∼10 21 cm −3 . Experimental studies of analogous BSO/SNO interfaces grown by molecular beam epitaxy confirm significant charge transfer from SNO to BSO. In situ angle-resolved X-ray photoelectron spectroscopy studies show an electron density of ∼4 × 10 21 cm −3 . The consistency of theory and experiments show that BSO/SNO interfaces provide a novel materials platform for low loss electron transport in 2DEGs.

Enhanced carrier densities in two-dimensional electron gas formed at BaSnO3/SrTaO3 and SrSnO3/SrTaO3 interfaces

“…Similarly, the total energy changes by less than 1.0 meV atom −1 when the k-point grids are increased to 14 × 14 × 14 and 14 × 14 × 1, for the bulk and interface, respectively. Using the DFT equilibrium structures, we calculated self-consistent ACBN0 Hubbard-U parameters for bulk BSO, SSO, and STaO (Hubbard-U parameters: BaSnO 3 : Ba = 3.96 eV, Sn = 0.04 eV, O = 8.8 eV; SrSnO 3 : Sr = 0.3 eV, Sn = 0.03 eV, O = 8.5 eV; SrTaO 3 : Sr = 0.01 eV, Ta = 1.1 eV, O = 7.6 eV), similar in magnitude to those reported previously for perovskites [16,42]. The computed Hubbard-U parameters of bulk BSO are identical to those reported in our previous work [16].…”

“…Using the DFT equilibrium structures, we calculated self-consistent ACBN0 Hubbard-U parameters for bulk BSO, SSO, and STaO (Hubbard-U parameters: BaSnO 3 : Ba = 3.96 eV, Sn = 0.04 eV, O = 8.8 eV; SrSnO 3 : Sr = 0.3 eV, Sn = 0.03 eV, O = 8.5 eV; SrTaO 3 : Sr = 0.01 eV, Ta = 1.1 eV, O = 7.6 eV), similar in magnitude to those reported previously for perovskites [16,42]. The computed Hubbard-U parameters of bulk BSO are identical to those reported in our previous work [16]. We computed the ACBN0 Hubbard-U parameters of bulk STaO and SSO for both cubic and orthorhombic phases and found that the Hubbard-U parameters depend only weakly on phase and octahedral rotation (∼0.1 eV).…”

“…The BSO/STaO heterostructures were generated by stacking six cubic (5 atoms) units of BSO and six cubic (5 atoms) units of STaO along the [001] direction, following previous work [16]. The cross-sectional area of the heterostructures was fixed at the ACBN0 equilibrium lattice parameter of the BSO substrate (a = 4.118 Å), following previous work [14,47], leading to an in-plane ∼1.9% tensile strain in the STaO layer.…”

“…One approach to generate high-mobility 2DEGs is to use materials in which the conduction band minimum (CBM) consists of spatially extended s-orbitals, improving wavefunction overlap and increasing mobility [14]. BaSnO 3 (BSO) is such a material and continues to attract much interest as a semiconducting electron acceptor [14][15][16]. Since the highly dispersive Sn-5s orbital in the BSO dominates the CBM, it has a comparatively low effective electron mass and high mobility [17].…”

“…Perovskites with octahedral VB cations in the d 1 electronic configuration are excellent electron donor materials due to their low work function and the large energy separation of O-2p and metals-d states [31]. Previous computational and experimental work has confirmed that SrNbO 3 (SNO) is the electron donor at the BSO/SNO heterostructure, creating at present the highest BSO-based charge carrier densities of n ∼ 10 21 cm −3 , ∼10% of the bulk carrier concentration [16]. Therefore, we expect to increase the sheet carrier density by replacing Nb-4d with spatially more extended Ta-5d electrons.…”