[Paper Review] Coherent Epitaxial Semiconductor-Ferromagnetic Insulator InAs/EuS Interfaces: Band Alignment and Magnetic Structure

Yu Liu, Alessandra Luchini+17 more|arXiv (Cornell University)|Aug 19, 2019

Electronic and Structural Properties of Oxides61 references4 citations

TL;DR

This study demonstrates lattice-matched, coherent epitaxial growth of InAs/EuS heterostructures, revealing a Fermi level near the InAs conduction band and within the EuS bandgap, preserving semiconducting behavior. Neutron and X-ray reflectivity show suppressed Eu moments at the interface, with no detectable induced moments in InAs despite ab initio predictions of a small exchange field, advancing high-quality spintronic platforms without external magnetic fields.

ABSTRACT

Hybrid semiconductor-ferromagnetic insulator heterostructures are interesting due to their tunable electronic transport, self-sustained stray field and local proximitized magnetic exchange. In this work, we present lattice matched hybrid epitaxy of semiconductor - ferromagnetic insulator InAs/EuS heterostructures and analyze the atomic-scale structure as well as their electronic and magnetic characteristics. The Fermi level at the InAs/EuS interface is found to be close to the InAs conduction band and in the bandgap of EuS, thus preserving the semiconducting properties. Both neutron and X-ray reflectivity measurements show that the ferromagnetic component is mainly localized in the EuS thin film with a suppression of the Eu moment in the EuS layer nearest the InAs. Induced moments in the adjacent InAs layers were not detected although our ab initio calculations indicate a small exchange field in the InAs layer. This work presents a step towards realizing high quality semiconductor - ferromagnetic insulator hybrids, which is a critical requirement for development of various quantum and spintronic applications without external magnetic fields.

Motivation & Objective

• To develop high-quality, lattice-matched semiconductor-ferromagnetic insulator heterostructures for spintronic applications.
• To understand the atomic-scale interface structure, band alignment, and magnetic properties at the InAs/EuS heterointerface.
• To investigate the presence and extent of induced magnetism in the InAs layer via proximity effect.
• To determine the spatial distribution of ferromagnetic moments in the EuS layer and their suppression near the interface.
• To validate theoretical predictions of exchange fields in InAs using experimental measurements.

Proposed method

• Epitaxial growth of InAs/EuS heterostructures on lattice-matched substrates to achieve coherent interfaces.
• X-ray and neutron reflectivity measurements to probe the density and magnetic depth profile of the EuS layer.
• Angle-resolved photoemission spectroscopy (ARPES) to determine the Fermi level position and band alignment at the interface.
• Ab initio density functional theory (DFT) calculations to predict exchange fields and electronic structure in the InAs layer.
• Analysis of reflectivity data using a self-consistent model to extract layer thickness, roughness, and magnetic moment depth profiles.
• Comparison of experimental results with theoretical predictions to assess the strength and spatial extent of proximity-induced magnetism.

Experimental results

Research questions

• RQ1 What is the band alignment at the coherent InAs/EuS heterointerface, and how does it affect electronic transport properties?
• RQ2 How is the ferromagnetic moment of EuS distributed across the thin film, particularly near the InAs interface?
• RQ3 Is there measurable induced magnetism in the InAs layer due to proximity to the ferromagnetic EuS?
• RQ4 To what extent is the EuS magnetic moment suppressed at the InAs/EuS interface?
• RQ5 How well do ab initio calculations predict the observed exchange field in the InAs layer?

Key findings

• The Fermi level at the InAs/EuS interface is positioned close to the InAs conduction band and within the bandgap of EuS, preserving semiconducting behavior.
• Neutron and X-ray reflectivity data show that the ferromagnetic component is primarily localized in the EuS layer, with a significant suppression of the Eu magnetic moment in the interfacial EuS layer.
• No detectable induced magnetic moments were observed in the adjacent InAs layers, despite ab initio calculations predicting a small exchange field.
• The interface is coherent and lattice-matched, enabling high-quality epitaxial heterostructures essential for quantum and spintronic devices.
• The absence of measurable induced moments suggests a weak proximity effect in InAs under the current experimental conditions.
• The results demonstrate a pathway toward field-free spintronic devices using semiconductor-ferromagnetic insulator heterostructures.