# Defect Tailoring in HfO2/Si Films upon Post-Deposition Annealing and Ultraviolet Irradiation
## 3 Results
### Optoelectronic Properties  
#### 3.4.1 Optical Fluorescence  
Figure 7a presents the fluorescence spectra of samples S1-S4 performed with an excitation wavelength of 270 nm. It can be observed that S1 and S2 samples present the lowest total fluorescence while S4 presents the highest, suggesting that this film has the highest defect density [17]. Emission maxima are evident at ca. 2.0 eV, 2.8 eV, 2.9 eV, 3.0 eV, and 3.8 eV. S1 and S2 spectra display fewer fluorescence features than S3 and S4. Figure 7b-e show the deconvoluted emission spectra of the samples.  
As shown in Figure 7a, the intensity and position of the fluorescence bands differ upon the film treatment. For semiquantitative characterization, Figure 8 presents the analysis  
Figure 6: Resistivity vs. bias voltage (**a**) and Schottky plots (**b**) of the HfO\({}_{2}\) samples. The lines in (**b**) are guides for the eye.  
Figure 7: Fluorescence spectra of (**a**) all the samples; (**b–e**) deconvoluted fluorescence spectra of (**b**) S1, (**c**) S2, (**d**) S3, and (**e**) S4.  
of the fluorescence peaks, where Figure 7a shows the peaks observed in each spectrum after deconvolution and the corresponding peak positions, and Figure 7b displays the areas of the peaks, normalized with the total area under the fluorescence emission curve, as a measure of the relative density of the electronic states contributing to the emission.  
As observed in Figure 8a, samples S1 (treated at 200 \({}^{\circ}\)C) and S2 (treated at 200 \({}^{\circ}\)C and then at 350 \({}^{\circ}\)C) display three emission peaks at ca. 2.5 eV, 2.8 eV, and 3.8 eV. Correspondingly, samples S3 and S4, which have UV treatment, display additional emission peaks at ca. 2 eV, 3 eV, and 3.5 eV. The peak at 2.8 eV presents an evident red shift from 2.82 eV (S1) to 2.71 eV (S4), while the position of the emission at 3.8 eV is almost invariant. These bands are congruent with those reported in [18].  
The emission band at 2.5 eV has been related either to hydrogen or chlorine defects [19], and it is only present before UV treatment. The emission band at 2.8 eV is characteristic of oxygen vacancy defects in HfO\({}_{2}\)[10]. On the other hand, the bands at 2.0, 3.0, and 3.5 eV, which appear only after treatment with UV light, may arise from dangling bonds and defect centers [1]. The increase in emissions due to the defects in S3 and S4 films corresponds with the XRD analysis, where it was found that S3 and S4 are amorphous. The band at 3.8 eV may arise from direct recombination from shallow states within the gap to the valence band [20] but has also been attributed to the OH radical within the structure [17].  
With respect to the relative contribution of each band to the fluorescence spectrum, Figure 8b presents the normalized areas of the fluorescence peaks. It can be observed that the dominant emissions in all the samples arise from the oxygen vacancies at 2.8 eV, although its relative intensity is variable with the sample treatment and the presence of additional emission bands upon UV treatment. For example, in S3, the 2.8 eV emission is lower than that in S4, but the emissions at 3.0, 3.5, and 3.8 eV are higher in S3 than in S4, indicating a reduction in the available states with the UV + annealing at 350 \({}^{\circ}\)C. The band at ca. 2.5 eV, related to hydrogen/chlorine defects, reduced its relative intensity with the increase in temperature from S1 to S2.  
The results indicate that the electronic structure of HfO\({}_{2}\) films is largely influenced by the UV treatment, which causes an increase in the defect states, which are partially reduced with the annealing temperature. More accurate defect engineering would be possible with optimized annealing temperature and time and UV irradiation times.  
Figure 8: (**a**) The position of the fluorescence peaks and (**b**) normalized intensity with respect to the total fluorescence area of the fluorescence peaks of samples S1–S4.