The Effect of Polar Fluctuation and Lattice Mismatch on Carrier Mobility at Oxide Interfaces

TL;DR

This study demonstrates that reducing lattice mismatch and controlling polar fluctuation at oxide interfaces significantly enhances carrier mobility, with specific critical thicknesses influencing the formation and peak of the 2DEG.

Contribution

It introduces a method to improve 2DEG mobility by using LSAT to reduce lattice mismatch and analyzes the effects of polar fluctuation and interface symmetry on carrier transport.

Findings

Carrier mobility increased 30-fold to 35,000 cm²V⁻¹s⁻¹ with reduced lattice mismatch.

Two critical thicknesses for 2DEG appearance and mobility peak at LSAT/SrTiO₃ (001).

Polar fluctuation from chemical composition affects 2DEG properties.

Abstract

Since the discovery of two-dimensional electron gas (2DEG) at the oxide interface of LaAlO3/SrTiO3, improving carrier mobility has become an important issue for device applications. In this paper, by using an alternate polar perovskite insulator (La0.3Sr0.7)(Al0.65Ta0.35)O3 (LSAT) for reducing lattice mismatch from 3.0% to 1.0%, the low-temperature carrier mobility has been increased 30 fold to 35,000 cm2V-1s-1. Moreover, two critical thicknesses for the LSAT/SrTiO3 (001) interface are found: one at 5 unit cell for appearance of the 2DEG, the other at 12 unit cell for a peak in the carrier mobility. By contrast, the conducting (110) and (111) LSAT/STO interfaces only show a single critical thickness of 8 unit cells. This can be explained in terms of polar fluctuation arising from LSAT chemical composition. In addition to lattice mismatch and crystal symmetry at the interface, polar fluctuation arising from composition has been identified as an important variable to be tailored at the oxide interfaces to optimise the 2DEG transport.