Gallium Sulfide as Phase-Change Material for Photonic Applications

Interest in phase-change materials (PCMs) is growing steadily because of their major role in the development of reconfigurable photonic devices. Nevertheless, conventional PCMs such as GST exhibit large optical losses in either or both states. Therefore, there is a need for alternative low-loss PCMs both in the visible and near-IR wavelengths. In light of this, other chalcogenides phase change materials, such as Sb₂S₃ or Sb₂Se₃, with band gaps at optical frequencies have been proposed as low-loss PCMs to be integrated in reconfigurable optical devices.<br/>Similarly, to Sb chalcogenides, layered monochalcogenides from group III (III= In, Ga) can display band gaps at optical frequencies. In these materials, it is known that as the chalcogen element decreases in atomic number (i.e. Te → Se → S), the bandgap of the material tends to increase (e.g. band gap energies of GaTe, GaSe and GaS are 1.7, 2.1 and 2.5eV respectively) as well as their air stability.<br/>In this contribution, we show the reversible amorphous to crystalline transition in phase change material GaS. We will present the result of the optimized deposition process of amorphous GaS stablishing some basic properties of the material such as Raman spectra, refractive index and absorption edge. We will additionally show the thermally activated amorphous-to-crystalline phase transformation of GaS demonstrating a refractive index contrast Δn ranging from 0.2 to 0.5 while maintaining negligible losses at telecommunication wavelengths. Finally, we will present the amorphization of the crystallized GaS using picosencond laser pulses identifying the energy density boundaries to achieve total amorphization with minimal ablation effects.<br/><br/>ACKNOWLEDGEMENTS: This work has been supported by the European Union’s Horizon 2020 research and innovation program under grant agreement no. 899598 – PHEMTRONICS. Y.G. acknowledge founding from founding from a Ramon y Cajal Fellowship (RYC2022-037828-I).