Facile fabrication of porous BixSy/Si photodetectors by one step laser ablation in liquid

In this study, facile bismuth sulfide (Bi_xS_y) porous nanostructures (NSs) were synthesized by the liquid-based pulsed laser ablation (PLAL) method. The Bi_xS_y nanostructures were formed by laser ablation of the bismuth (Bi) target within 1 M of thiourea [SC (NH₂)₂] aqueous solution, along a fixed 400 laser pulses. The influence of laser fluence on the microstructural, morphological, chemical, optical, and electrical features of Bi_xS_y porous film has been systematically examined. X-ray diffraction (XRD) analysis confirmed that all synthesized Bi_xS_y nanoparticles (NPs) demonstrated a poly-crystalline nature along orthorhombic crystal orientation. As the fluence of laser amplified from 6.37 J/cm²/pulse to 15.92 J/cm²/pulse, the attained direct bandgap of Bi_xS_y reduced from 1.8 to 1.69 eV. Photoluminescence (PL) measurements showed a single emission peak at 672, 677, 712, and 729 nm for Bi_xS_y NSs prepared at 6.37, 9.55, 12.74, and 15.92 J/cm²/pulse, respectively. Raman spectroscopy revealed three vibrational modes positioned around 294, 510, and 654 cm⁻¹. Field emission scanning electron microscope (FE-SEM) images displayed the construction of a porous, grid-like nanostructure, with particle sizes ranging from 34.08 nm to 44.65 nm for sample fabricated with 15.92 J/cm²/pulse fluence. The dark I-V features of Al/n-Bi_xS_y/p-Si/Ag heterostructured photodetectors demonstrated rectifying behavior. Under incident light, the photo current-voltage (I-V) properties indicated high photosensitivity. A device attained at fluence of 12.74 J/cm²/pulse exhibited the highest responsivity (1.139 A/W) and specific detectivity (1.68 × 10^¹³ Jones) at 375 nm. Additionally, the highest external quantum efficiency (EQE) of 376.52% was achieved at 375 nm for the same photodetector. The time-resolved analysis (ON/OFF states) are also demonstrated by means of laser fluence.