Thickness-dependent optical properties and ultrafast carrier dynamics of 2D non-layered β-In2S3

Non-layered 2D materials, such as indium sulfide (In2S3), possess distinctive properties due to their unsaturated surface bonds and atomically thin structures, rendering them highly promising for state-of-the-art optoelectronic applications. Herein, we conduct a comprehensive investigation into the optical characteristics and ultrafast carrier dynamics of β-In2S3 nanoflakes. Through thickness-dependent Raman, photoluminescence (PL), and absorption spectra, we reveal the critical role of thickness in tuning the optical properties of β-In2S3. Notably, β-In2S3 exhibits broad PL emission and a robust nonlinear optical response in second-harmonic generation (SHG), largely attributed to inherent defect states. Thickness-dependent SHG surpasses conventional odd/even layer limitations, highlighting β-In2S3’s unique optical versatility. Ultrafast carrier dynamics further unveil two distinct defect-mediated recombination processes: a fast non-radiative pathway and a slower radiative pathway, both accelerating with increasing thickness, as revealed by thickness-dependent transient absorption spectroscopy. This finding underscores the significant modulation of recombination lifetime by varying the thickness of β-In2S3. These insights not only emphasize the versatility of β-In2S3 for optoelectronic applications but also pave the way for its integration into next-generation devices, offering a promising avenue for advancing the field of optoelectronics.