Tuning the Interface Conductivity of LaAlO₃/SrTiO₃ Using Ion Beams: Implications for Patterning

Abstract

Patterning of the two-dimensional electron gas formed at the interface of two band insulators such as LaAlO3/SrTiO3 is one of the key challenges in oxide electronics. The use of energetic ion beam exposure for engineering the interface conductivity has been investigated. We found that this method can be utilized to manipulate the conductivity at the LaAlO3/SrTiO3 interface by carrier localization, arising from the defects created by the ion beam exposure, eventually producing an insulating ground state. This process of ion-beam-induced defect creation results in structural changes in SrTiO3 as revealed by the appearance of first-order polar TO2 and TO4 vibrational modes which are associated with Ti-O bonds in the Raman spectra of the irradiated samples. Furthermore, significant observation drawn from the magnetotransport measurements is that the irradiated (unirradiated) samples showed a negative (positive) magnetoresistance along with simultaneous emergence of first-order (only second order) Raman modes. In spectroscopic ellipsometry measurements, the optical conductivity features of the irradiated interface are broadened because of the localization effects, along with a decrease of spectral weight from 4.2 to 5.4 eV. These experiments allow us to conclude that the interface ground state (metallic/insulating) at the LaAlO3/SrTiO3 can be controlled by tailoring the defect structure of the SrTiO3 with ion beam exposure. A resist-free, single-step direct patterning of a conducting LaAlO3/SrTiO3 interface has been demonstrated. Patterns with a spatial resolution of 5 μm have been fabricated using a stencil mask, while nanometer scale patterns may be possible with direct focused ion beam writing.

Accumulation, inversion, and depletion layers inSrTiO3

“…For any temperature this field is much larger then the critical field D c and Eq. (19) 11,51,52 . In order to describe the electron concentration n(x) for such a surface charge density, σ = 0.05e/a 2 , one can still use Eq.…”

Charge Transfer and Orbital Reconstruction in Strain-Engineered (La,Sr)MnO3/LaNiO3 Heterostructures

“…3 A minor variation of interfacial electronic state often causes a dramatic change of interfacial properties, and thus the understanding and manipulation of the electronic behavior would advance the use of interface in oxide-based electronics. 7,8,[10][11][12] Among oxide interfaces, heterostructures composed of magnetic materials offer an excellent illustration of the richness of interfacial phenomena and hold the potential for applications in spin valves, magnetic recording and reading heads. 2,13,14 The exchange bias, one of the outcomes of exchange anisotropy at the interface between a ferromagnetic (FM) and an antiferromagnetic (AFM) components, has also been discovered at the interface between ferromagnetic and paramagnetic (PM) oxide components in recent decades, 2,13,14,15 attracting a large amount of experimental and theoretical work to discern the nature of this interfacial exchange coupling.…”

Effects of surface defects on two-dimensional electron gas at NdAlO3/SrTiO3 interface

“…With the breakthrough of cutting-edge thin-film epitaxial techniques like pulsed laser deposition and molecular-beam epitaxy, high quality heterointerfaces based on perovskite transition metal oxides have been achieved experimentally and revealed to exhibit a large number of fascinating electrical and magnetic properties1. A prominent example is the discovery of the two-dimensional electron gas (2-DEG) at the interface between two band insulators, polar LaAlO 3 (LAO) and non-polar SrTiO 3 (STO)2.…”