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arXiv · 2511.22484

Reststrahlen band and optical bandgaps in semiconducting CrN films

Duc V. Dinh·Xiang Lü·Oliver Brandt·Dilara Sen·Olivia Fairlamb·Frank Peiris·Farihatun Lima·Alexander Bordovalos·Suresh Chaulagain·Ambalanath Shan·Nikolas J. Podraza
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Abstract

We present a comprehensive optical characterization of 200-nm-thick CrN(111) films grown simultaneously on Al$_2$O$_3$(0001) and AlN/Al$_2$O$_3$(0001) using plasma-assisted molecular beam epitaxy. Spectroscopic ellipsometry, spanning the far-infrared to ultraviolet range (0.04 - 5.5 eV), is conducted at room temperature to determine the optical constants $n$ and $k$ of the films. Spectral fits reveal two interband transitions at approximately 0.35 and 0.60 eV. In the infrared range, the ellipsometry data also reveals a pronounced Reststrahlen band stemming from transversal and longitudinal optical phonons at approximately 403 and 629 cm$^{-1}$, respectively. The relative static and high-frequency permittivities are estimated to be about 39 and 15, respectively. A Born effective charge of approximately 2.7, extracted from the far-infrared region, indicates that CrN is partially ionic.

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Duc V. Dinh, Xiang Lü, Oliver Brandt, Dilara Sen, Olivia Fairlamb, Frank Peiris, Farihatun Lima, Alexander Bordovalos, Suresh Chaulagain, Ambalanath Shan, Nikolas J. Podraza. 2025-11-27. Reststrahlen band and optical bandgaps in semiconducting CrN films. https://arxiv.org/abs/2511.22484

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