Influence of laser energy on CuO@ZnO nanoparticles for enhancing spectral responsivity

Abstract

In this work, silicon n-type (111) was photoelectrochemically etched to create porous silicon (PS) substrates. Pulsed laser ablation (PLA) was utilized to synthesize copper oxide (CuO) nanoparticles as a core enveloped by zinc oxide (ZnO) nanoshells (CuO@ZnO) nanostructures. The core–shell structure of CuO@ZnO nanoparticles is synthesized utilizing different pulsed laser ablation energy and subsequently incorporated onto PS substrates. The research study examined the impact of laser energy on the structural, morphological, optical, photodetector, and electrical aspects of the fabricated devices. The X-ray diffraction studies for CuO@ZnO nanoparticles reveal a phase consistent with hexagonal wurtzite for ZnO nanoparticles and a monoclinic crystal structure for CuO nanoparticles. X-ray diffraction reveals a significant broad diffraction peak at 28.4° for porous silicon. The CuO@ZnO nanostructures have similar spherical grains distributed randomly, whereas PS possesses a sponge-like architecture, as evidenced by the SEM images. TEM images indicate that core–shell nanoparticles display the particle size distribution at average diameters of 30, 70, and 19 nm for those synthesized employing pulses of laser light with energies of 500, 700, and 900 mJ, respectively. TEM images also reveal the dark central area for copper oxide nanoparticles and the relatively lighter outside section for the zinc oxide nanoshell, thereby confirming its core–shell configuration. UV–visible absorption spectroscopy and photoluminescence were utilized to examine the optical properties of the produced specimens. The findings indicated that variations in the energy gap are associated with changes in the laser energy utilized in sample preparation. UV–visible absorption and photoluminescence analysis revealed a band gap of energies ranging between 3 to 2.41 eV with variations in laser energy. The manufactured samples’ current–voltage (J-V) density properties were examined in illuminated and non-illuminated conditions. The J-V characteristic curves indicate that elevating laser energies increased sample current density, especially when the specimen was generated at 900 mJ. A photocurrent density demonstrated a substantial correlation with a rise within the incident intensity of light, particularly when the specimen was produced at 700 mJ, encouraging using it for the photodetector device. Nonetheless, adjusting the laser energy led to changes in the photocurrent of all the CuO@ZnO NPs/PS samples. Also, incorporating CuO@ZnO nanoparticles in the PS samples resulted in a significant improvement in the responsivity (R_λ) relative to a sample of porous silicon-only. CuO@ZnO nanoparticles can absorb light across an extensive spectrum of wavelengths, visible to nearly infrared. The maximum detectivity (D*) value was noted during a laser pulse energy of 900 mJ. The noted behaviors can be ascribed to changes in the size or morphology of CuO@ZnO nanoparticles arising from differences in laser energy during their manufacture. Moreover, a fabricated photodetector demonstrated improved enhanced of quantum efficiency, particularly within the visible spectrum.