Elsevier

Optik

Volume 209, May 2020, 164585
Optik

Original research article
Optical modulation at the interface between silicon and a phase change material

https://doi.org/10.1016/j.ijleo.2020.164585Get rights and content

Abstract

Thin layers of phase change materials are investigated theoretically and experimentally as way to modulate the properties of light interacting with silicon at a planar interface. By inducing a phase transition in vanadium dioxide films, the resulting changes in refractive index modulate the injection of light into silicon and the ejection out of it. Internal reflection of light propagating inside silicon causes the polarization state to be altered during the phase transition. Possible applications to silicon photonics are discussed.

Section snippets

Theory

As shown in Fig. 1, the system under study is composed of silicon and air interfaced with a layer of phase change material, namely VO2, with thickness d. The plane of incidence defines polarization states TM (or p) and TE (or s). Injection and ejection of light are quantified as the fraction of light intensity crossing the interface when the light source is in air or inside silicon, respectively. Reflectance and polarization modulation refer to light’s internal reflection in silicon.

It is

Results and discussions

To investigate modulation of transmittance across the air/VO2/silicon interface, we determine the highest possible modulation obtained by varying the angle of incidence and film thickness. For simplicity, we chose to fix the wavelength at 1550 nm, but similar results were obtained for wavelengths in the 1100 nm <λ< 1800 nm range. In Fig. 2, for all combinations of θi and d spanning 0θi90o and 0d300 nm (to best reflect typical VO2 films thicknesses), the minimum value of Tmin is plotted

Experiment

As a proof of concept, we created samples of VO2 on silicon by using reactive magnetron sputtering to deposit metallic vanadium films on p-doped silicon substrates (15 Ω cm resistivity). Oxidation to VO2 was achieved by exposing metallic films to an oxygen-rich environment at a temperature of 500 °C and at a pressure of 150 mtorr for one hour. Using an infrared ellipsometer, transmittance and external reflectance were measured at 1550 nm for different angles of incidence, with VO2 in its

Conclusions

Phase change materials such as VO2 interfaced with silicon can provide tunable functionalities for applications in silicon photonics, and possibly other devices such as tunable photovoltaic cells. While phase change materials have been studied extensively in the context of silicon waveguide and resonators, we showed that light interactions across a single layer also provides control capabilities for injecting light into silicon (from air), ejection of light from silicon, and for the modulation

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

We acknowledge funding by the National Science and Engineering Research Council of Canada.

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