Evaluating the quantum confinement effects modulating exciton and electronic band structures of two-dimensional layered MoSSe films and their photodetection potentials

Emerging two-dimensional ternary transition metal dichalcogenide alloys have attracted much attention for their unique optical and optoelectronic properties, making them ideal candidates for optoelectronic applications. However, a comprehensive understanding of their quantum confinement effects and photoelectronic response characteristics remains crucial for device optimization and performance enhancement. In this study, we employed various spectroscopic techniques to investigate the optical properties and electronic band structures of molybdenum sulfide selenide (MoSSe) films with different layer numbers (4–11 layers). Our results revealed the splitting of Raman modes and shifting of phonon vibrational frequencies with increasing thickness, suggesting that MoSSe has strong interactions within the lattice. The A_1g and E_2g¹ modes were mainly shifted by internal strain and dielectric screening effect versus thickness, respectively. The redshift phenomenon of A and B excitons with increasing thickness was attributed to the leading effect of quantum confinement on exciton properties and optical band gaps. We observed a strong decrease in the direct bandgap spectral weight in photoluminescence (PL) when the layer number increased from 4 to 5. In addition, we have fabricated MoSSe photodetectors that exhibit a broadband response in the visible wavelength band of 350–800 nm. Furthermore, the observed enhancement in photocurrent and responsivity with increasing film thickness underscored the potential of MoSSe-based devices for practical optoelectronic applications. This research contributes to advancing our fundamental understanding of MoSSe materials and paves the way for the design and development of high-performance optoelectronic devices.