Synthesis of HgI2 Nanoparticles and Nanorods by Laser Ablation in Liquid for Photodetector Applications: Effect of Laser Fluence

In this study, mercury iodide (HgI2) nanoparticles (NPs) were synthesized by pulsed laser ablation in ethanol at laser fluences of 22.9, 33.1, and 43.3 J/cm2. The effect of laser fluence on the structural and optical properties of HgI2 NPs was studied. X-ray diffraction findings reveal that all synthesized HgI2 samples were polycrystalline in nature with orthorhombic structure. Absorption peak was appeared at 474 nm and the optical energy gap of HgI2 NPs decreases from 2.13 to 2.05 eV as laser fluence increased from 22.9 to 43.3 J/cm2. Zeta potential (ZP) results confirm that the nanoparticles synthesized at 22.9 and 33.1 J/cm2 have high degree of stability. Fluorescence measurements show the presence of several emission bands. Raman spectra of HgI2 NPs show the presence of six vibration modes centered at 15, 29, 37, 44, 51, and 70 cm−1. Fourier transform infrared (FT-IR) results show the presence of two bonds, namely, C–O and Hg-I. Transmission Electron Microscope (TEM) results showed that the formation of spherical nanoparticles for sample prepared at 22.9 J/cm2, 25–75 nm in size. While the nanoparticles synthesized with 33.1 and 43.3 J/cm2 exhibit nanorods and nanotubes morphologies, respectively. The dark I–V characteristics of β-HgI2 NPs/Si heterojunction photodetectors show rectification properties and the junction quality depends on the laser fluence and the best junction characteristics was obtained for heterojunction prepared at 33.1 J/cm2. The white light photosensitivity of the HgI2/p-Si photodetectors was measured at reverse bias under different intensities. The maximum responsivity reached was 3.39A/W at 450 nm for photodetector prepared at 33.1 J/cm2.