Synthesis of ZnSe thin films by solution-processed spin coating method for photonic integration applications

This investigation introduces a novel method for the fabrication of ZnSe thin films on glass substrates through the spin coating technique which employs thiol-amine cosolvents. The thiol-amine co-solvent system efficiently dissolves several metal and metal chalcogenide precursors, facilitating cost-effective, and low-temperature solution-based deposition compatible with flexible substrates. The synthesized ZnSe thin films underwent air annealing at temperatures between 250 and 350 °C, thereby improving their structural and optical characteristics. The polycrystalline nature of ZnSe was elucidated via X-ray diffraction (XRD) analysis, while scanning electron microscopy (SEM) assured the rise of surface smoothness and uniformity with annealing temperature. Energy-dispersive spectroscopy (EDS) analysis indicated near-stoichiometric ZnSe composition, and Fourier-transform infrared (FTIR) spectroscopy identified Zn–Se stretching vibrations in the 960–1120 cm⁻¹ range. The optical data demonstrated high transmittance with an optical bandgap of 3.32–3.85 eV. Furthermore, optical data of ZnSe were embarked for computation of Ge-on-ZnSe waveguide with SiO₂ cladding for long-wave infrared (LWIR) light. The waveguide showed a remarkable power confinement factor (PCF) of ~ 0.99 with nearly 1 dB/cm loss at a laser wavelength of 8 μm. These outputs are highly optimistic for the fabrication of solution-processed ZnSe for LWIR photonic integration.