Colloidal synthesis of cesium iodide nanocrystals for visible-enhanced photodetection applications

In this study, cesium iodide (CsI) nanoparticles were synthesized for the first time by pulsed laser ablation in ethanol at various laser fluences. The structural and optical properties of the CsI nanoparticles were studied as a function of laser fluence. The x-ray diffraction (XRD) results confirm the formation of crystalline CsI with a cubic structure along (110) plane. The optical absorbance spectra showed two absorption peaks at 291 and 363 nm. The optical energy gap of CsI NPs decreases as laser fluence increases. Transmission electron microscope studies show that the synthesized nanoparticles have a spherical shape and the mean particle size prepared at 22.9, 33.1 and 43.3 J/cm2 was 23, 25, and 28 nm, respectively. Scanning electron microscope results reveal the formation of nanosized spherical CsI nanoparticles. The fluorescence emission data of CsI shows two main bands centered at 339 nm and 387 nm. Raman spectra show three Raman peaks located at 15, 26 and 44 cm−1. The zeta potential results confirm that the CsI NPs prepared at 33.1 J/cm2 have good stability. The current-voltage characteristics of CsI/Si heterojunctions show rectification properties, and the illuminated current-voltage shows that the maximum photocurrent was found for a photodetector fabricated at 33.1 J/cm2. The maximum responsivity and detectivity of the photodetector are 1.66 A/W and 5.5 × 1012 Jones at 400 nm, respectively, for a photodetector prepared at 33.1 J/cm2. A quantum efficiency of 5.16 × 102% at 400 nm is reached for a photodetector prepared at 33.1 J/cm2. The Hall effect shows that the synthesized CsI NPs are p-type and the highest hole mobility was found for a sample prepared at 33.1 J/cm2.