Optical Properties of Chalcogenide Thin Films

Chalcogenide thin films, composed of compounds containing sulphur, selenium or tellurium combined with elements such as arsenic or germanium, exhibit unique optical behaviours that underpin a broad spectrum of technologies in infrared photonics and optoelectronics. Their wide transparency window in the mid-infrared region, high refractive index and strong nonlinear response arise from the high polarizability of chalcogen elements and the covalent network structure. In as-deposited films, subtle variations in stoichiometry, structural ordering and deposition parameters lead to pronounced changes in optical bandgap, absorption coefficient and dispersion. The ability to tailor refractive index through compositional tuning or post-deposition treatments enables gradient-index designs, waveguide integration and antireflective coatings. Nonlinear phenomena such as two-photon absorption and third-order susceptibility are enhanced in thin-film geometries, facilitating ultrafast all-optical switching and supercontinuum generation. Thermal annealing or laser processing can induce controlled crystallisation, modulating bandgap and refractive index to suit applications in photonic integrated circuits, infrared lenses and sensors. Ongoing research balances the demands of low optical loss, high nonlinearity and environmental stability, driving advances in deposition techniques, in situ characterisation and device integration on silicon and other substrates.

Research from Nature Portfolio

Recent studies have demonstrated that incorporation of bismuth into indium selenide films combined with precise annealing protocols can drastically enhance both linear and nonlinear optical characteristics. Films annealed at higher temperatures transition from amorphous to partially crystalline phases rich in Bi2Se3, yielding a reduction in optical bandgap and an increase in static refractive index. Concurrently, third-order nonlinear susceptibility and nonlinear refractive index values rise significantly with bismouth content, highlighting potential for mid-infrared modulators and photonic switches. Surface morphology analyses confirm phase transformation without detrimental agglomeration, suggesting compatibility with photovoltaic and optoelectronic integration strategies.

Optical Properties of Chalcogenide Thin Films publication trend

The graph below shows the total number of articles in optical properties of chalcogenide thin films across all publications each year (not limited to Nature Index journals).

Technical terms

Thin film: A layer of material with thickness in the nanometre to micrometre range, often exhibiting size-dependent optical properties.

Refractive index: A dimensionless measure of how light propagates through a medium, describing the ratio of phase velocity in vacuum to that in the material.

Optical bandgap: The energy threshold at which a material begins to strongly absorb photons, marking the transition between valence and conduction bands.

Nonlinear optical susceptibility (χ(3)): A parameter quantifying a material’s intensity-dependent response to light, governing third-order phenomena such as self-phase modulation.

Annealing: A controlled heating process that alters the microstructure of a material, often used to induce crystallisation or relieve internal stresses.

References

1. Erbium-doped chalcogenide glass thin film on silicon using femtosecond pulsed laser with different deposition temperatures. Applied Physics A (2018).
2. Ultrafast all-optical chalcogenide glass photonic circuits. Optics Express (2007).
3. Improvement of Swanepoel method for deriving the thickness and the optical properties of chalcogenide thin films.. Optics Express (2017).
4. Observation of high nonlinearity in Bi doped BixIn35-xSe65 thin films with annealing. Scientific Reports (2021).