J. Eur. Opt. Society-Rapid Publ. 2026, 22, 33 Ó The Author( s), published by EDP Sciences, 2026 https:// doi. org / 10.1051 / jeos / 2026036 Available online at: https:// jeos. edpsciences. org
EOSAM 2025 Guest editors: Omar El Gawhary, Stefan Witte, Ignacio Moreno
Journal of the European Optical Society-Rapid Publications
RESEARCH ARTICLE
Atomic layer deposition for hafnium oxide-based meta-optics in the ultraviolet spectral range
Thomas Siefke 1, 2, 3, *
, Kristin Gerold 1, 2, Svetlana Shestaeva 2, Pallabi Paul 1, 2, Shawon Alam 4, Daniel Franta 5, Adriana Szeghalmi 1, 2, Sven Schröder 2, and Stefanie Kroker 6, 7, 8 1 Friedrich-Schiller-University, Institute of Applied Physics, Albert-Einstein-Strasse 15, 07745 Jena, Germany 2 Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Albert-Einstein-Str. 7, 07745 Jena, Germany 3 Ernst-Abbe-Hochschule Jena, University of Applied Sciences, Carl-Zeiss-Promenade 2, 07745 Jena, Germany 4 Karlsruhe Institute of Technology( KIT), Kaiserstraße 12, 76131 Karlsruhe, Germany 5 Department of Plasma Physics and Technology, Faculty of Science, Masaryk University, Kotlářská 2, 61137 Brno, Czechia 6 TU Braunschweig, Institute of Semiconductor Technology, Hans-Sommer-Str. 66, 38106 Braunschweig, Germany 7 TU Braunschweig, LENA Laboratory for Emerging Nanometrology, Langer Kamp 6a / b, 38106 Braunschweig, Germany 8 Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
Received 30 January 2026 / Accepted 4 April 2026
Abstract. Hafnium oxide( HfO 2) is a high-index dielectric material of growing importance for optical coatings and meta-optical components operating from the ultraviolet( UV) to the visible spectral range. Its large bandgap, chemical stability, and compatibility with established semiconductor processes make it particularly attractive for applications requiring low absorption and precise thickness control. In this work, we investigate the optical material properties of HfO 2 thin films deposited by plasma-enhanced atomic layer deposition( PEALD). The complex refractive index is experimentally determined over a broad spectral range extending from the vacuum ultraviolet( 140 nm) to the visible( 600 nm) by combining spectroscopic ellipsometry, spectrophotometry, and infrared ellipsometry. A comprehensive dispersion model is employed to extract consistent optical constants and thickness values. The results highlight the suitability of PEALD-grown HfO 2 films for advanced optical and meta-optical applications.
Keywords: Hafniumoxide, meta-optics, ultra violet, refractive index, atomic layer deposition.
1 Introduction
Hafnium oxide( HfO 2) hasattractedsignificant attention over the past two decades as a functional material in both microelectronics and photonics. In microelectronic devices, HfO 2 is well established as a high-permittivity( high-k) dielectric replacing SiO 2 in advanced metal-oxide-semiconductor field-effect transistors [ 1 – 3 ]. Beyond its electronic functionality, the optical properties of HfO 2, namely its high refractive index, wide optical bandgap, and high transparency from the ultraviolet to the infrared, render it attractive for optical coatings, interference filters, and dielectric metasurfaces [ 4 – 7 ]. In particular, the demand for optical components such as wire grid polarizer [ 8, 9 ], meta lenses [ 10 ] or diffractive optical elements [ 11 ] or grating couplers in photonic integrated circuits [ 12 ] operating in the ultraviolet and vacuum ultraviolet spectral ranges has increased substantially due to applications in spectroscopy
* Corresponding author: thomas. siefke @ uni-jena. de
– especially in quantum technologies [ 13 – 15 ] – space optics, and high-resolution microscopy. For these applications, materials must combine low optical absorption with high refractive index contrast and excellent environmental stability. HfO 2 fulfills these requirements and offers superior laser-induced damage threshold( LIDT) [ 16, 17 ] as well as resistance to radiation-induced damage [ 18, 19 ] and chemical degradation and corrosion compared to many alternative high-index oxides. A large variety of deposition techniques have been employed for HfO 2 thin films, such as electron beam evaporation [ 20, 21 ], magnetron sputtering [ 22 ], ion beam sputtering [ 23, 24 ], sol-gel [ 25 – 27 ] and atomic layer deposition( ALD) [ 28 – 33 ]. Among these, ALD is particularly suitable for the fabrication of HfO 2 thin films with precisely controlled thickness and excellent structural conformality. The self-limiting surface reactions inherent to ALD enables uniform coatings on both planar as well as three-dimensional nanostructured substrates, which is essential for emerging meta-optical concepts relying on subwavelength structuring.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License( https:// creativecommons. org / licenses / by / 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.