Fabrication of High-Performance ZnO Nanostructure/Si Photodetector by Laser Ablation

The potential for improving the performance of a silicon photodetector using a nanostructured window layer has drawn significant attention due to its large surface area and superior properties. In this study, zinc oxide nanoparticles were synthesized through laser ablation in water at various laser fluences. X-ray diffraction (XRD) analysis revealed that the ZnO nanoparticles are crystalline with a hexagonal wurzite structure, and scanning electron microscopy (SEM) confirmed that the synthesized ZnO nanoparticles have a spherical morphology, with sizes ranging from 45 to 85 nm, depending on the laser fluence. Agglomeration of nanoparticles is observed at high laser fluence. The energy gap of ZnO nanoparticles increased from 3.47 to 3.64 eV as the laser fluence increased from 3.6 to 4.7 J/cm 2 . Photoluminescence (PL) investigations revealed that the presence of single emission peak observed at 361 nm. Raman spectra indicated the presence of E2, E1 (LO), E1 (TO), and E1(LO) + E1(TO) vibration modes. Electrical properties, including electrical resistivity, mobility, current–voltage, and capacitance–voltage characteristics, were investigated as a function of laser fluence. The best ideality factor and built-in potential were 2.8 and 1.35 V, respectively, for the nanostructured ZnO/Si heterojunction prepared at a laser fluence of 4.2 J/cm 2 . The capacitance–voltage characteristics proved that the fabricated junctions are abrupt. The impact of laser fluence on the responsivity, external quantum efficiency, and detectivity was studied in the visible and near-infrared range. The photodetector fabricated at 4.2 J/cm 2 exhibited a responsivity of 9.9 A/W at 450 nm, a quantum efficiency of 2.951 × 10 2 %, and a detectivity of 4.3 × 10 12 Jones at 450 nm, at a bias voltage of –5 V.