Carrier‐Density Control of the SrTiO₃ (001) Surface 2D Electron Gas studied by ARPES

Abstract

Keywords: strontium titanate, angle resolved photoemission spectroscopy, two-dimensional electron gas, oxygen vacancies Combining the tunability of semiconductor heterostructures with the rich properties of correlated electron systems is a central goal in materials science. The two-dimensional electron gas (2DEG) observed at the LaAlO 3 /SrTiO 3 (LAO/STO) interface [1] emerged as a particularly promising model system in this regard since it combines high mobility with properties such as gate-tunable superconductivity that cannot be realized in conventional semiconductor heterostructures or bulk correlated electron systems. [2][3][4][5] The interface 2DEG resides solely in STO and can be stabilized in different ways. These include interfacing STO with other crystalline insulating materials such as spinel Al 2 O 3 or perovkite GdTiO 3 , [6,7] deposition of amorphous overlayers, [Y. Chen et al, Nano Lett. 2011, 11, 3774. 8,9] and electrolyte gating. [10] A similar 2DEG has also been observed on the bare surface of STO following irradiation with

Temperature-dependent band structure ofSrTiO3interfaces

“…[24][25][26] Band structure calculations for LAO/STO interfaces [17][18][19] predict that the majority of the conducting electrons reside in the TiO 2 planes adjacent to the interface, and occupy bands with d xy symmetry, while occupied bands with d xz and d yz symmetry extend farther into STO. Because of the differences in their spatial extent, the d xy bands at the interface should be much more strongly affected by interfacial roughening than the d xz /d yz bands, 17 and indeed Hall measurements have been interpreted in terms of a two-component system with two distinct mobilities.…”

Effect of a skin-deep surface zone on the formation of a two-dimensional electron gas at a semiconductor surface

“…Two-dimensional electron gases (2DEGs) occurring at surfaces of semiconductors have been studied for many years due to their rich phenomenology and extreme technological relevance [1][2][3][4][5][6][7][8][9][10][11][12][13]. The 2DEGs arise following subsurface confinement of conduction electrons caused by an electric field.…”

Room temperature 2D electron gas at the (001)-SrTiO3 surface

“…This shows that the beam exposure has a greater effect on the creation of the 2DEG than the annealing used to prepare the surface and that the 2DEG is populated by electrons freed following the creation of oxygen vacancies at the surface. 9,10 Spectra of the Ti 2p core-level (not shown) exhibited a higher Ti 3þ component after the beam exposure, reinforcing the fact that the beam is responsible for reduced Ti 4þ rather than the annealing. 10 This sensitivity of the 2DEG to the oxygen partial pressure may limit the possibilities of realistic electronic devices to oxide structures with buried interfaces such as LAO/STO.…”

“…The highest spectroscopic resolution, allowing one to resolve 2D and 3D band characters, calculate the Fermi surface (FS) volume, and estimate the electron effective mass, is obtained at low temperature, typically 10-20 K. 9,12 Nevertheless, any realistic oxide based electronics must obviously work at room temperature (RT). Therefore, the study of the 2DEG band structure at the surface of STO at RT has to be conducted.…”

“…From the fit, the effective mass can be estimated as 0.2m e , in agreement with the values obtained by SantanderSyro 4 and McKeown-Walker. 9 The 2D carrier density, defined by n 2D ¼ k 2 F =2p, can be obtained by measuring the Fermi momenta (k F ). The measured k F ¼ 0.169 Å À1 leads to a 2D carrier density of 4.57 Â 10 13 cm…”