Composition, structure, and semiconducting properties of Mg<i> _x </i>Zr_2−<i>x</i>N₂ thin films

Abstract

Synthesis and characterization of Mg&lt;em&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/em&gt;Zr&lt;sub&gt;2–&lt;em&gt;x&lt;/em&gt;&lt;/sub&gt;N&lt;sub&gt;2&lt;/sub&gt; (0.5 ≤ x ≤ 1.8) thin films deposited by reactive magnetron co-sputtering in nitrogen plasma is reported. Composition measurements show that nitrides with low oxygen content (less than 1%) can be formed up to x = 1.0, at which point an increase in oxygen content is observed. Up to composition of x &gt; 1.6 the Mg&lt;em&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/em&gt;Zr&lt;sub&gt;2–&lt;em&gt;x&lt;/em&gt;&lt;/sub&gt;N&lt;sub&gt;2&lt;/sub&gt; thin films form in a rocksalt-derived crystal structure, as revealed by X-ray diffraction measurements. At x &gt; 1.6 the films rapidly oxidize. The lattice constant of the stoichiometric MgZrN&lt;sub&gt;2&lt;/sub&gt; composition is a = 4.537 Å, and only small changes in lattice parameter are observed with changing composition. Electrical conductivity decreases by several orders of magnitude with increasing Mg-content. The conductivity of Mg-rich (x ≥ 1) films increases with increasing measurement temperature, indicating semiconducting character of Mg-rich Mg&lt;em&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/em&gt;Zr&lt;sub&gt;2–&lt;em&gt;x&lt;/em&gt;&lt;/sub&gt;N&lt;sub&gt;2&lt;/sub&gt;. As a result, optical absorption measurements of these Mg-rich samples show a clear absorption onset at 1.8 eV, also indicative of semiconducting behavior.