Energy-tunable 1064 nm pulsed laser ablation in liquid synthesis of Al₂O₃ nanoparticles for interface-engineered high broadband Si photodetectors
摘要
Aluminum oxide (Al₂O₃) nanoparticles were synthesized using a clean, surfactant-free pulsed laser ablation in liquid (PLAL) route and directly integrated onto silicon substrates to fabricate Al₂O₃/Si heterojunction photodetectors. A 1064 nm Q-switched Nd: YAG laser was employed at pulse energies of 400, 500, 600, 700, and 800 mJ to systematically investigate the influence of laser energy on nanoparticle formation, interfacial properties, and device performance. X-ray diffraction confirmed the formation of rhombohedral Al₂O₃, with improved crystalline ordering as the laser energy increased. The crystallite size calculated from the dominant Al₂O₃ (104) reflection increased from 14.98 nm at 400 mJ to 43.71 nm at 800 mJ, indicating enhanced atomic rearrangement and crystallite growth under high-energy ablation conditions. FE-SEM analysis revealed spherical Al₂O₃ nanoparticles with energy-dependent morphology and partial agglomeration; the average particle size varied within the nanoscale range and reached approximately 59.7 nm for the 800 mJ sample, which exhibited a more homogeneous and well-defined surface morphology. Cross-sectional FE-SEM showed Al₂O₃ layer thicknesses of about 117 and 143 nm for the 400 and 800 mJ samples, respectively. UV–Vis spectroscopy showed strong absorption in the ultraviolet region. At the same time, the optical bandgap decreased from 3.41 to 3.31 eV as laser energy increased, suggesting defect-assisted electronic transitions and laser-induced modification of the nanostructure. EDS analysis confirmed the high purity of the deposited Al₂O₃ nanostructures. Electrical measurements of the Al₂O₃/Si heterojunctions showed rectifying diode-like behavior, with ideality factors ranging from 1.55 to 4.84 and Schottky barrier heights between 0.41 and 0.48 eV, indicating non-ideal thermionic emission influenced by interface states and barrier inhomogeneity. Under illumination, the devices exhibited an increase in photocurrent with increasing light intensity and reverse bias voltage. Spectral measurements revealed a broadband photoresponse with distinct responsivity features near 450, 600, and 800 nm, primarily attributed to wavelength-dependent absorption and carrier generation in silicon. The device fabricated at 500 mJ exhibited optimal photodetection performance at 1000 nm, achieving a responsivity of approximately 0.87 A/W, a detectivity of approximately 68 Jones, and an external quantum efficiency of approximately 115%. The novelty of this work lies in establishing a direct correlation among 1064 nm PLAL pulse energy, Al₂O₃ nanoparticle structure, Al₂O₃/Si interface behavior, and broadband photodetector performance, thereby demonstrating a simple, chemical-free strategy for engineering Si-based optoelectronic devices.