Structural peculiarities of $\epsilon$-Fe${}_2$O${}_3$ / GaN epitaxial layers unveiled by high-resolution transmission electron microscopy and neutron reflectometry

Abstract

The present paper is dedicated to the structural study of crystallographic peculiarities appearing in epitaxial films of metastable epsilon iron oxide ($\epsilon$-Fe${}_2$O${}_3$) grown by pulsed laser deposition onto a semiconductor GaN (0001) substrate. The columnar structure of the nanoscale $\epsilon$-Fe${}_2$O${}_3$ films has been for the first time investigated using high resolution electron microscopy (HRTEM) direct space technique complemented by reciprocal space methods of high-energy electron diffraction and color-enhanced HRTEM image Fourier filtering. The study of $\epsilon$-Fe${}_2$O${}_3$ / GaN interface formation has been further expanded by carrying out a depth resolved analysis of density and chemical composition by neutron reflectometry and energy-dispersive X-ray spectroscopy. The obtained results shed light onto the properties and the origin of the enigmatic few-nanometer thick low density transition layer residing at the $\epsilon$-Fe${}_2$O${}_3$ / GaN interface. A detailed knowledge of the properties of this layer is believed to be highly important for the development of $\epsilon$-Fe${}_2$O${}_3$ / GaN heterostructures that can potentially become part of the iron-oxide based ferroic-on-semiconductor devices with room temperature magneto-electric coupling.

arXiv comment14 pages, 9 figures

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