Stoichiometry dependence of potential screening atLa(1−δ)Al(1+δ)O

Abstract

Hard x-ray photoelectron spectroscopy (HAXPES) and variable kinetic energy x-ray photoelectron spectroscopy (VKE-XPS) analyses have been performed on 10 unit cell La (1−δ) Al (1+δ) O 3 films, with La:Al ratios of 1.1, 1.0, and 0.9, deposited on SrTiO 3 . Of the three films, only the Al-rich film was known to have a conductive interface. VKE-XPS, coupled with maximum entropy analysis, shows significant differences in the compositional depth profile between the Al-rich, the La-rich, and stoichiometric films; significant La enrichment at the interface is observed in the La-rich and stoichiometric films, while the Al-rich shows little to no intermixing. Additionally, the La-rich and stoichiometric films show a high concentration of Al at the surface, which is not observed in the Al-rich film. HAXPES valence band (VB) analysis shows a broadening of the VB for the Al-rich sample relative to the stoichiometric and La-rich samples, which have insulating interfaces. This broadening is consistent with an electric field across the Al-rich film. These results are consistent with a defect-driven electronic reconstruction.2

Epitaxial Oxides on Semiconductors: From Fundamentals to New Devices

“…This common explanation is based on a discontinuity in the polarization at the interface, which is often referred to as the polar catastrophe . Competing explanations suggest that ionic defects such as oxygen vacancies, or cation intermixing are the dominant mechanisms behind the emergence of 2DEGs. The observation of 2DEGs at oxide interfaces between an amorphous oxide and crystalline STO seems to preclude the scenario of an electronic reconstruction .…”

Predictive Control over Charge Density in the Two-Dimensional Electron Gas at the Polar-NonpolarNdTiO3/SrTiO3Interface

“…However, consensus has not yet been reached concerning the mechanism(s) of interfacial conduction, which has been linked to non-stoichiometry in the LAO film. [1][2][3][4][5] Starting with the earliest observations, it has been hypothesized that conductivity arises from an electronic reconstruction (ER) to alleviate the "polar catastrophe" which accompanies the formation of an abrupt interface. 7 Extrinsic factors, such as unintentional doping via cation intermixing and oxygen vacancy generation, have also been considered in light of the actual, as opposed to idealized properties of the interface.…”

“…[1][2][3][4][5][6] Polar/non-polar interfaces can be categorized as those with the same B-site cation, and those with different B-site cations. The former include RTiO 3 on SrTiO 3 where R = La, Gd and Nd.…”

Recent applications of hard x-ray photoelectron spectroscopy

“…However, the results were again discussed only in relation to this model, with added considerations for photo-induced charge carriers and defects which may offset the electric field. In contrast, a small but measurable electric field exists in Alrich LAO deposited on STO as shown in Figure 19 [109]; such a field had also been observed in cross sectional STM [110] and electrical measurements [111]. The electric field was observed in the valence band region only.…”