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

## TL;DR

This paper describes a simple method to create porous bismuth sulfide nanostructures using laser ablation in liquid, which are used to make efficient photodetectors.

## Contribution

A one-step laser ablation method is introduced to fabricate BixSy/Si photodetectors with high photosensitivity and quantum efficiency.

## Key findings

- BixSy nanostructures with a porous, grid-like morphology were successfully synthesized using pulsed laser ablation in thiourea solution.
- Photodetectors made at 12.74 J/cm²/pulse fluence showed the highest responsivity (1.139 A/W) and detectivity (1.68 × 10¹³ Jones) at 375 nm.
- The highest external quantum efficiency of 376.52% was achieved at 375 nm for the same photodetector.

## Abstract

In this study, facile bismuth sulfide (BixSy) porous nanostructures (NSs) were synthesized by the liquid-based pulsed laser ablation (PLAL) method. The BixSy 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 BixSy porous film has been systematically examined. X-ray diffraction (XRD) analysis confirmed that all synthesized BixSy 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 BixSy reduced from 1.8 to 1.69 eV. Photoluminescence (PL) measurements showed a single emission peak at 672, 677, 712, and 729 nm for BixSy 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-BixSy/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 × 10¹³ 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.