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.
Highlights
HfO2 is a dielectric material with a wide band-gap, high dielectric constant, high refractive index, and high thermal stability that is widely used in the preparation of optical coatings and microelectronic films [1,2,3]
For optical thin-film applications, it is widely used in the preparation of optical films with low absorption and high damage threshold for high-power pulsed laser systems [4,5,6,7,8]
We present the absorption, photoluminescence, and crystallization properties of two kinds of
Summary
HfO2 is a dielectric material with a wide band-gap, high dielectric constant, high refractive index, and high thermal stability that is widely used in the preparation of optical coatings and microelectronic films [1,2,3]. HfO2 is the most promising alternative to SiO2 in metal-oxide-semiconductor (MOS) microelectronic devices [9]. Studies have shown that there are various defects in HfO2 films, such as oxygen vacancies and charge traps [9,10,11,12,13,14,15,16]. These defects affect the absorption loss and laser damage threshold of the optical coatings, and the leakage current and carrier mobility of the MOS. The investigation of the defects in HfO2 films is of great significance for the preparation of high-performance laser optical thin films and microelectronic films
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