Vanadium oxide metal-insulator phase transition in different types of one-dimensional photonic microcavities

Scotognella, Francesco

doi:10.3389/fphot.2023.1081521

ORIGINAL RESEARCH article

Front. Photon., 17 March 2023
Sec. Optical Nanostructures
Volume 4 - 2023 | https://doi.org/10.3389/fphot.2023.1081521

Vanadium oxide metal-insulator phase transition in different types of one-dimensional photonic microcavities

Francesco Scotognella*

Dipartimento di Fisica, Politecnico di Milano, Milan, Italy

The optical properties of vanadium dioxide (VO₂) can be tuned via metal-insulator transition. In this work, different types of one-dimensional photonic structure-based microcavities that embed vanadium dioxide have been studied in the spectral range between 900 nm and 2000 nm. In particular, VO₂ has been sandwiched between: i) two photonic crystals made of SiO₂ and ZrO₂; ii) two aperiodic structures made of SiO₂ and ZrO₂ that follow the Thue-Morse sequence; iii) two disordered photonic structures, made of SiO₂ and ZrO₂ in which the disorder is introduced either by a random sequence of the two materials or by a random variation of the thicknesses of the layers; iv) two four material-based photonic crystals made of SiO₂, Al₂O₃, Y₂O₃, and ZrO₂. The ordered structures i and iv show, respectively, one and two intense transmission valleys with defect modes, while the aperiodic and disordered structures ii and iii show a manifold of transmission valleys due to their complex layered configurations. The metal-insulator transition of VO₂, controlled by temperature, results in a modulation of the optical properties of the microcavities.

Introduction

Crystalline vanadium dioxide (VO₂) shows a thermochromic phase transition around 68°C (341 K) (Morin, 1959). The phase transition is related to a structural crystal change from a monoclinic insulating phase to a tetragonal (rutile) metallic phase (Briggs et al., 2010; Currie et al., 2017). From an optical point of view, the phase transition of VO₂ results in a change from an insulating semi-transparent material to a metallic more lossy and reflective material (Verleur et al., 1968; Currie et al., 2017). The VO₂ phase transition can be exploited for several applications, such as smart windows, steep-slope devices for micro-electronics, neuromorphic computing devices, reconfigurable radiofrequency switches, optical limiters, and metasurfaces (Liu et al., 2018; Lu et al., 2021; Li et al., 2023; Tognazzi et al., 2023).

A method to utilize the VO₂ switchable optical properties is the integration of such material in photonic crystals (John, 1987; Yablonovitch, 1987; Joannopoulos, 2008). In photonic crystals, the periodic modulation of the refractive index in one, two or three dimensions gives rise to energy regions in which light is not transmitted through the crystal. The integration of materials with switchable optical properties in the infrared, such as photochromic polymers (Toccafondi et al., 2014) and infrared plasmonic nanomaterials (Guo et al., 2016; Kriegel et al., 2016), in one-dimensional photonic crystals has been proposed previously (Kriegel and Scotognella, 2018). Furthermore, the deposition of a VO₂ layer onto a one-dimensional photonic crystal has been theoretically studied by Rashidi et al. (2018) and experimentally studied by Singh et al. (Singh et al.(2020).

In this work, different types of one-dimensional photonic microcavities (Boucher et al., 2009) are proposed, in which a layer of VO₂ is embedded between two photonic crystals, two aperiodic Thue-Morse photonic structures, two disordered photonic structures, and two four-material based photonic crystals. The wavelength dependent refractive indexes of all the employed materials have been implemented. The light transmission of the microcavities has been simulated via the transfer matrix method. The modulation of the transmission spectra of the microcavities due the VO₂ metal-insulator phase transition has been highlighted.

Materials and methods

The light transmission of the different microcavities in the spectral range between 900 nm and 2000 nm has been studied with the transfer matrix method (Born et al., 1999; Xiao et al., 2016; Paternò et al., 2019). The system is glass/multilayer/air with light impinging the sample surface orthogonally. The characteristic matrix of the multilayer is written as

M = [\begin{array}{c} M_{11} & M_{12} \\ M_{21} & M_{22} \end{array}] = \prod_{k = 1}^{N} [\begin{array}{c} \cos (\frac{2 π}{λ} n_{k} (λ) d_{k}) & - \frac{i}{n_{k} (λ)} \sin (\frac{2 π}{λ} n_{k} (λ) d_{k}) \\ - i n_{k} (λ) \sin (\frac{2 π}{λ} n_{k} (λ) d_{k}) & \cos (\frac{2 π}{λ} n_{k} (λ) d_{k}) \end{array}] (1)

with k=(1,…,N) and N number of layers. The parameters $d_{k}$ and $n_{k} (λ)$ are the thickness and the wavelength dependent refractive index of the kth layer, respectively. The light transmission is written as

T = \frac{n_{0}}{n_{g}} {|\frac{2 n_{g}}{(M_{11} + M_{12} n_{0}) n_{g} + (M_{21} + M_{22} n_{0})}|}^{2} (2)

with $n_{g}$ the refractive index of glass and $n_{0}$ the refractive index of air ( $n_{g} = 1.46; n_{0} ≅ 1$ ). The light transmission has been calculated in the selected spectral range with steps of 0.25 nm. The wavelength dependent refractive index $n_{k} (λ)$ can be written with the Sellmeier equation

n_{k}^{2} (λ) - 1 = \sum_{j^{'} = 1} \frac{A_{j^{'}} λ^{2}}{λ^{2} - B_{j}^{2}} (3)

The parameters $A_{j}$ and $B_{j}$ are reported in Table 1.

TABLE 1

TABLE 1. Parameters of the Sellmeier equation for SiO₂, Al₂O₃, Y₂O₃, and ZrO₂.

The wavelength dependent refractive indexes of vanadium dioxide in the metal phase and in the insulating phase (30 °C) and in the metallic phase (100 °C) have been taken from Ref. (Briggs et al., 2010). The employment of the two refractive indexes in the transfer matrix method allows to simulate the optical properties of the different photonic structures in the two temperature regimes.

Results and discussion

In Figure 1 the light transmission spectrum for the microcavity (SiO₂/ZrO₂)₅/VO₂/(ZrO₂/SiO₂)₅ is shown. The black solid curve is related to VO₂ in the insulating phase, while the blue dashed curve is related to VO₂ in the metallic phase. The two phases correspond to a temperature of the material of 30°C for the insulating phase and a temperature of 100 °C for the metallic phase, respectively, as reported in Ref. (Briggs et al., 2010). In the microcavity the thickness of the silicon dioxide layers is 220 nm, the thickness of the zirconium dioxide layers is 165 nm, while the thickness of the vanadium dioxide layers is 55 nm.

FIGURE 1

FIGURE 1. Light transmission spectra for the microcavity (SiO₂/ZrO₂)₅/VO₂/(ZrO₂/SiO₂)₅ with VO₂ in the insulating phase (at 30°C, black solid curve) and in the metallic phase (at 100°C, blue dashed curve).

In the microcavity configuration, the insulating VO₂ based microcavity shows a defect mode at around 1,250 nm within the photonic band gap of the structure (i.e., the intense transmission valley between 1,100 nm and 1,600 nm). The intensity of the defect mode is in agreement with experimental values shown in microcavities for coherent photoluminescence (Chiasera et al., 2019). On the other hand, for light filtering, the defect mode intensity is not high enough, and higher values are required for this type of application. The defect mode is magnified in the inset of Figure 1. Instead, for the metallic VO₂ based microcavity the defect mode is suppressed. Noteworthy, the transmission at wavelengths longer than 1,600 nm is weaker in the metallic VO₂ phase because of its infrared absorption.

In Figure 2 the transmission spectrum for the aperiodic microcavity that follows the Thue-Morse sequence is depicted. The VO₂ layer is sandwiched between two photonic structures with the sequence of layers ABBABAABBAABABBABAABABBAABBABAAB (Steurer and Sutter-Widmer, 2007) (A = SiO₂; B = ZrO₂). The layer thicknesses are the same ones of the periodic structure. The black solid curve is related to VO₂ in the insulating phase, while the blue dashed curve is related to VO₂ in the metallic phase. The transmission spectra are slightly modified with the VO₂ from the insulating to the metallic phase, with the suppression of peaks around 1,100 and 1,600 nm.

FIGURE 2

FIGURE 2. Light transmission spectra for the
Thue-Morse aperiodic microcavity
ABBABAABBAABABBABAABABBAABBABAAB/
VO₂/ABBABAABBAABABBABAABABBAABBABAAB
(A = SiO₂; B = ZrO₂) with VO₂ in the insulating phase (at 30°C, black solid curve)
and in the metallic phase (at 100°C, blue dashed curve).

In Figure 3A the transmission spectra for the disordered microcavity, in which VO₂ is embedded between one-dimensional disordered photonic structures are shown (Wiersma et al., 2005; Wiersma, 2013). The proposed structure follows the sequence BBABBAABBBABBBBA/VO₂/BABAABBBBABBBABA. Also in this case, the layer thicknesses are the same ones of the periodic structure and the black solid curves correspond to the insulating phase of VO₂, while the blue dashed curves to the metallic phase of VO₂. The transmission spectrum with VO₂ in the insulating phase shows eight peaks in the studied range (900–2000 nm). With the transition from insulator to metal the suppression of most of the transmission peaks is noticeable.

FIGURE 3

FIGURE 3. (A) Light transmission spectra for the disordered microcavity BBABBAABBBABBBBA/VO₂/
BABAABBBBABBBABA (A = SiO₂; B = ZrO₂) with VO₂ in the insulating phase (at 30°C, black solid curve) and in the metallic phase (at 100°C, blue dashed curve). (B) Light transmission spectra for the microcavity (SiO₂/ZrO₂)₅/VO₂/(ZrO₂/SiO₂)₅, in which a random variation of the thicknesses is introduced, with VO₂ in the insulating phase (at 30°C, black solid curve) and in the metallic phase (at 100°C, blue dashed curve).

In Figure 3B is shown the transmission spectra of the microcavity (SiO₂/ZrO₂)₅/VO₂/(ZrO₂/SiO₂)₅, in which a random variation of the thicknesses is introduced (Faist et al., 1989; Chiasera et al., 2015). For the SiO₂ layers the thickness follows $[2 \times (110 \pm n)]$ , while for the ZrO₂ layers the thickness follows $[1.5 \times (110 \pm n)]$ , where n is an integer random number between 0 and 20. The transmission spectrum for the microcavity with vanadium dioxide in the insulating phase shows a manifold of transmission valleys and peaks. The transition from insulator to metal suppresses several transmission peaks, as, for example, the narrow peak at 1,200 nm.

In Figure 4A the transmission spectrum of the four material-based microcavity (SiO₂/Al₂O₃/Y₂O₃/ZrO₂)₆/VO₂/(ZrO₂/Y₂O₃/Al₂O₃/SiO₂)₆ is shown. The thickness of SiO₂ layers is 275.9 nm, the thickness of Al₂O₃ layers is 228.6 nm, the thickness of Y₂O₃ layers is 210.5 nm, the thickness of ZrO₂ layers is 190.5 nm, and the thickness of VO₂ layers is 45.9 nm. As shown in previous reports, four-material photonic crystals show a manifold of gaps (Kriegel and Scotognella, 2015). In fact, with this structure, in the wavelength interval between 900 nm and 2000 nm two intense photonic band gaps are observable, compared to the single photonic band gap of the microcavity (Figure 1). In this case, the defect modes of the two photonic band gaps show a red shift and a remarkable intensity increase. In Figure 4B the transmission spectrum of the four material-based microcavity is shown in logarithmic scale to highlight the large modulation depth of the transmission peak at around 1,100 nm and 1,600 nm for the metallic phases of vanadium dioxide.

FIGURE 4

FIGURE 4. (A) Light transmission spectra for the
four-material photonic crystal based microcavity
(SiO₂/Al₂O₃/Y₂O₃/ZrO₂)₆/
VO₂/(ZrO₂/Y₂O₃/Al₂O₃/SiO₂)₆ with VO2 in the insulating phase
(at 30°C, black solid curve) and in the metallic
phase (at 100°C, blue dashed curve). (B) Light transmission spectra for the four-material photonic crystal based microcavity in logarithmic scale.

Conclusion

In this work it has been studied the light transmission of different one-dimensional photonic microcavities that embed vanadium dioxide by means of the transfer matrix method. The four types of microcavities include periodic photonic crystals, aperiodic structures, disordered structures, and four-material-based photonic crystals. The different structures have been chosen in order to exploit their particular optical properties: An intense photonic bandgap with a defect for the microcavities including photonic crystals, a multiplicity of transmission valleys in the case of the microcavity with aperiodic structures, the occurrence of several transmission peaks, or a broader photonic band gap, in the case of microcavities with disordered structures, a doublet of photonic band gaps in the case of microcavities with four-material-based photonic structures. The transmission of VO₂ from insulator to metal, achievable via a temperature increase, leads to a modulation of the transmission spectra, noticeable with shifts and suppressions of transmission peaks. The modulation of the transmission spectra of the microcavities can be exploited for smart windows and temperature-controlled switches. Moreover, the photonic structure can be also used as temperature sensor since it has been studied by Currie et al. the temperature dependent refractive index dispersion of vanadium dioxide (Currie et al., 2017).

Data availability statement

The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.

Author contributions

FS is the sole author of the manuscript. FS conceived the idea, performed the simulations, analysed the data, wrote the manuscript.

Funding

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 816313).

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

References

Born, M., Wolf, E., Bhatia, A. B., Clemmow, P. C., Gabor, D., Stokes, A. R., et al. (1999). Principles of optics: Electromagnetic theory of propagation, interference and diffraction of light. 7th ed. Cambridge, UK: Cambridge University Press. doi:10.1017/CBO9781139644181

ORIGINAL RESEARCH article

Vanadium oxide metal-insulator phase transition in different types of one-dimensional photonic microcavities

Introduction

Materials and methods

Results and discussion

Conclusion

Data availability statement

Author contributions

Funding

Conflict of interest

Publisher’s note

References

This article is part of the Research Topic

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