【International Papers】Liquid-Metal Fabrication of Ultrathin Gallium Oxynitride Layers with Tunable Stoichiometry

      Researchers from the University of Lyon have published a dissertation titled "Liquid-Metal Fabrication of Ultrathin Gallium Oxynitride Layers with Tunable Stoichiometry " in Advanced Photonics Research.

Abstract

      The synthesis of nanometer-thick (≈3 nm) gallium oxynitride (GaO_xN_y) layers with a variable stoichiometry is reported. The approach primarily exploits the liquid metal chemistry (LMC) technique and promises easier integration of 2D materials onto photonic devices compared to traditional top-down and bottom-up methods. The fabrication follows a two-step process, involving first liquid metal-based printing of a nanometer-thick layer of gallium oxide (Ga₂O₃), followed a plasma-enhanced nitridation reaction. Control over nitridation parameters (plasma power, exposure time) allows adjustment of the GaO_xN_y layer's composition, granting access to compounds with distinct optical properties (e.g., a 20% index variation), as demonstrated by ellipsometry and density functional theory (DFT) simulations. DFT provides a microscopic understanding of the effect of the bond polarization and crystallinity on the optical properties of GaO_xN_y compounds. These findings expand the knowledge of ultrathin GaO_xN_y alloys, which are poorly studied with respect to their gallium nitride (GaN) and Ga₂O₃ counterparts. They also represent an essential step toward integrating such 2D materials into photonic chips and offer new opportunities to improve the performance of hybrid optoelectronic devices.

Figure 1 Synthesis process of large-area ultrathin GaN nanosheets. a) Schematic illustration of the Cabrera–Mott oxidation that occurs at the surface of liquid metals in the presence of oxygen followed by the printing technique used to exfoliate 2D oxides from molten metal. The liquid metal droplet is squeezed between two substrates allowing the transfer of the Ga₂O₃ layer. b) Synthesis process of the ultrathin GaN nanosheet from ultrathin layer of Ga₂O₃, utilizing a microwave-activated nitrogen/hydrogen plasma conducted in a cylindrical cavity plasma reactor. c) Optical image of the synthesized GaN on SiO₂/Si, confirming the presence of an ultrathin and homogeneous layer reaching several millimeters in lateral size.

Figure 2 Material characterization of ultrathin Ga₂O₃ (before nitridation (a and c)) and ultrathin GaN (after the nitridation (b and d)) on a SiO₂/Si substrate. a,c) XPS results of the ultrathin Ga₂O₃ for the spectral regions of interest, around (a) the Ga 2p peak and (c) the O 1s peak. b,d) XPS result for the the ultrathin GaN around (b) the Ga 2p peak and (d) the O 1s peak.

Paper Link：https://doi.org/10.1002/adpr.202300252