Near-ultraviolet absorption annealing in hafnium oxide thin films subjected to continuous-wave laser radiation

Abstract

Hafnium oxide (HfO 2) is the most frequently used high-index material in multilayer thin-film coatings for high-power laser applications ranging from near-infrared to near-ultraviolet (UV). Absorption in this high-index material is also known to be responsible for nanosecond-pulse laser-damage initiation in multilayers. In this work, modification of the near-UV absorption of HfO 2 monolayer films subjected to irradiation by continuouswave (cw), 355-nm or 351-nm laser light focused to produce power densities of the order of ∼100 kW∕cm 2 is studied. Up to a 70% reduction in absorption is found in the areas subjected to irradiation. Temporal behavior of absorption is characterized by a rapid initial drop on the few-tens-of-seconds time scale, followed by a longerterm decline to a steady-state level. Absorption maps generated by photothermal heterodyne imaging confirm the permanent character of the observed effect. Nanosecond-pulse, 351-nm and 600-fs, 1053-nm laser-damage tests performed on these cw laser-irradiated areas confirm a reduction of absorption by measuring up to 25% higher damage thresholds. We discuss possible mechanisms responsible for near-UV absorption annealing and damage-threshold improvement resulting from irradiation by near-UV cw laser light.

Assessment of the Morphological, Optical, and Photoluminescence Properties of HfO2 Nanoparticles Synthesized by a Sol–Gel Method Assisted by Microwave Irradiation

“…The fact that the quantum size effect was not observed by us (nor by others) could be explained by the presence of several intermediary energy levels within the band gap because of intrinsic (trap sites) defects, self-trapped excitons, and extrinsic defects. ,, …”

Investigation of laser annealing mechanisms in thin film coatings by photothermal microscopy

“…As one of the processes ruled out is the heating of the material by free carrier absorption, the temperature driven annealing predicted by full atomistic simulations of the annealing of amorphous SiO 2 [19] has been discarded. The passivation of the defects and reduction of the absorptance can be attributed to the trapping of the electrons in deep states, leaving the shallow states unoccupied as suggested in [12]. The fact that the shallow defects are not completely passivated by this mechanism might be explained in this model by the fact that not enough unoccupied deep traps are available.…”

“…The other possibility is that the defects simply anneal by the temperature rise. As direct absorption from shallow states cannot heat the material to high enough temperature [12], a significant temperature rise, if present, must be originated in free carrier absorption. Other options are multiphoton absorption from deeper lying interband states, and combination of several of the mentioned mechanisms.…”

Tuning the Electrical Parameters of p-NiOx-Based Thin Film Transistors (TFTs) by Pulsed Laser Irradiation

“…In continuation of the previous work in [23], laser irradiation was also employed to study its effects in modifying the intrinsic properties of metallic [24,25], semiconducting [26][27][28][29], superconducting [30], multiferroic [31] and ceramic [32] thin films. In [33], the most frequently used high dielectric material, hafnium oxide (HfO 2 ), was subjected to irradiation by a continuous wave laser with a wavelength of 355 nm to analyze the temporal behavior of absorption annealing. In [34], the postdeposition annealing of tin oxide (SnO 2 ) thin films by ultra-short laser pulses resulted in a change in the refractive index and conductivity of the films.…”