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The Optical Absorption and Photoluminescence Characteristics of Evaporated and IAD HfO2 Thin Films

1
Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, China
2
Chinese Academy of Sciences, Beijing 100039, China
3
School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China
*
Author to whom correspondence should be addressed.
Coatings 2019, 9(5), 307; https://doi.org/10.3390/coatings9050307
Received: 4 April 2019 / Revised: 28 April 2019 / Accepted: 5 May 2019 / Published: 8 May 2019
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Abstract

HfO2 thin films are extensively applied in optical coatings and microelectronic devices. However, film defects, which are vital to the performance of the thin films, are still under intense investigation. In this work, the absorption, photoluminescence, and crystallization characteristics of HfO2 films prepared by electron-beam evaporation and ion-assisted deposition are investigated in detail. Experimental results showed that high-temperature thermal annealing in air resulted in a reduced absorption coefficient, an increased bandgap width, and an increased degree of crystallization. After thermal annealing, an absorption shoulder near 5.8 eV was caused by excitons in the films, which were independent of oxygen vacancy defects and crystallization. Under 6.4 eV (193 nm) laser excitation, the photoluminescence spectrum showed five emission peaks for HfO2 films both with and without thermal annealing. The emission peak near 4.4 eV was generated by the self-trapped exciton, and the peak near 4.0 eV was related to the OH group in the film. The oxygen vacancy defect-induced absorption of HfO2 films in a broad spectral range significantly increased when HfO2 film was re-annealed in Ar gas after first being annealed in air, while the photoluminescence spectrum showed no significant change, indicating that the emission peaks at 2.3, 2.8, and 3.4 eV were not related to oxygen vacancy defects. View Full-Text
Keywords: HfO2 thin films; optical absorption; photoluminescence; electron-beam deposition; ion-assisted deposition (IAD) HfO2 thin films; optical absorption; photoluminescence; electron-beam deposition; ion-assisted deposition (IAD)
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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MDPI and ACS Style

Kong, M.; Li, B.; Guo, C.; Zeng, P.; Wei, M.; He, W. The Optical Absorption and Photoluminescence Characteristics of Evaporated and IAD HfO2 Thin Films. Coatings 2019, 9, 307.

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