What question did this study set out to answer?

This research aims to characterize the optical properties of CrN films and identify their optical bandgaps.

April 12, 2026Physical Review Materials0 citationsOpen Access

Reststrahlen band and optical bandgaps in semiconducting CrN films

DDDuc V. Dinh XLXiang Lü OBOliver Brandt

Key Points

This research aims to characterize the optical properties of CrN films and identify their optical bandgaps.
Grew 200-nm-thick CrN films on substrates using plasma-assisted molecular beam epitaxy.
Conducted spectroscopic ellipsometry from 0.04 to 5.5 eV at room temperature.
Analyzed data to extract optical constants and identify spectral features.
Identified interband transitions at approximately 0.35 and 0.60 eV.
Observed a Reststrahlen band appearing at around 403 and 629 cm−1 due to optical phonons.
Estimated relative static permittivity at about 39 and high-frequency permittivity at 15.

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 reveal 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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