Synthesis and characterization of broadband white light emission from ZnO nanostructures on porous silicon

Abstract

Porous silicon (PSi) substrates were fabricated via electrochemical anodization of boron-doped p-type Si (100) wafers (1.0−10.0 Ω⋅cm). ZnO nanostructures were subsequently grown on PSi and on ZnO-seeded Si (seeded Si) substrates via hydrothermal synthesis at 85°C using a precursor of 0.075 mol/L zinc acetate and 0.025 mol/L hexamethylenetetramine (HMTA) in 150 mL of deionized water. Growth durations of 15, 30, 45, and 60 minutes were used for seeded Si, while a fixed 15-minute duration was used for PSi. Post-growth annealing at 450°C for 15 minutes was applied to one ZnO-PSi sample and compared to an as-grown control. Structural and optical properties were characterized by X-ray diffraction (XRD), Raman spectroscopy, and room-temperature photoluminescence (PL) spectroscopy. Annealing transformed the as-grown yellow-orange emission into broadband white-light photoluminescence spanning the blue (≈423 nm), green (≈539 nm), and red (≈685 nm) regions simultaneously, arising from the superposition of ZnO defect emission and the PSi S-band. These results demonstrate that hydrothermally grown ZnO on PSi, combined with moderate post-growth annealing, constitutes a silicon-compatible platform for broadband visible light emission.