Theoretical Investigation of the Band Alignment at the LaAlO3/SrTiO3 Interface
- PDF / 391,689 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 84 Downloads / 199 Views
0966-T07-33
Theoretical Investigation of the Band Alignment at the LaAlO3/SrTiO3 Interface Jaekwang Lee and Alexander A. Demkov Department of Physics, The University of Texas, 26th and Speedway, C1600, Austin, TX, 78712 ABSTRACT Epitaxially grown oxide superlattices are attracting considerable attention due to their unusual properties and possible applications ranging from sensors to electronic devices [1]. We report a first-principles study of interfaces in the epitaxial LaAlO3/SrTiO3 system within density functional theory. We consider the electronic structure of the n-type interface, and compute the band alignment. INTRODUCTION Recently, Ohtomo el al. reported the growth of atomically precise, lattice matched superlattices consist of alternating layers of LaAlO3 (LAO) and SrTiO3 (STO) [2-3]. It turns out that the interface between the two oxides is metallic, and depending on the termination (e.g. TiO2/LaO or SrO/AlO2) could be either n- or p-type. They measured metallic conductivity and high electron mobility by Hall measurement at the n-type LAO-STO interface. They report, however, that presumably due to the charge compensation the p-type interface becomes insulating This suggests that in the case of Figure 1 The structure of an ABO3 perovskite oxides two different compensatory mechanisms are perovskite cell: A atom is at the cube corner, B atom is in the center, and at play at the heterojunction. For the n-type LAO/STO oxygen atoms are in the face centers. interface it is purely electronic involving mixed valence Ti ions, while for the p-type it is an ionic reconstruction involving oxygen vacancies. The bulk structural and electronic properties of STO and LAO have been studied theoretically [4-6], and so has been the surface of STO [7-8]. Much less is known about the surface of LAO, and we are unaware of any calculations of the work function. In this paper we report first principles calculations using density functional theory (DFT) of the work functions of LAO and STO, and the band alignment at the n-type LAO/STO interface. THEORY Table I: Elastic constants for bulk STO and LAO
Lattice const. STO (Å) LAO (Å) Elastic const.(STO) B (1011Pa) 11
C11 , C12 (10 Pa) Elastic const.(LAO) B (1011Pa) 11
C11 , C12 (10 Pa)
*Referece [15]
Theoretical
Experimental*
3.874 3.744
3.905 3.789
2.07 1.00 , 4.21
2.47 1.03, 3.2
2.28 3.82, 1.50
Density functional calculations [9-10] are done within the local density approximation using the projected augmented wave (PAW) pseudopotentials [11] as implanted in the VASP code [12]. The exchange-correlation effects are taken into account within the Perdew-Wang scheme [13]. A standard plane wave basis set is used with a kinetic energy cutoff of 600eV. For the Brillouin zone integration we use an 8×8×8 and 8×8×1 k-
point meshes for cubic bulk cells, and slabs or hetero-structures, respectively. The calculations are converged to 10-6 eV/cell and the structures are relaxed until forces are less than 10-2 eV/Å. Surface calculations are performed in slab geometry with seven layers
Data Loading...
