Self-biased photodetector using 2D layered bismuth triiodide (BiI3) prepared using the spin coating method.

Layered bismuth triiodide (BiI3) is a 2D material that has emerged as an ideal choice for optical sensors. Although BiI3 has been prepared using vacuum-based deposition techniques, there is a dearth of research studies on synthesizing this material using chemical route. The present work uses a facile spin coating method with varying rotation speeds (rpm) to fabricate BiI3 material thin films for photodetection applications. The structural, optical, and morphological study of BiI3 thin films prepared at 3000-6000 rpm were investigated. XRD analysis indicates formation of BiI3 films and revealed that BiI3 has a rhombohedral crystal structure. FESEM analysis showed that BiI3 films prepared at different rpm are homogeneous, dense, and free from cracks, flaws, and protrusions. In addition, films show an island-like morphology with grain boundaries having different grain sizes, micro gaps, and the evolution of the granular morphology of BiI3 particles. The UV spectroscopy and photoluminescence analysis revealed that BiI3 films strongly absorb light in the visible region of spectra with a high absorption coefficient of ∼104 cm-1, have an optical band gap of ∼1.51 eV. A photodetector was realised using fabricated BiI3 film obtained at an optimum spin speed of 4000 rpm. It showed rapid rise and decay times of 0.4 s and 0.5 s, a responsivity of ∼100 µA W-1, external quantum efficiency of 2.1 × 10-4%, and detectivity of ∼3.69 × 106 Jones at a bias voltage of 0 V. Our results point towards a new direction for layered 2D BiI3 materials for the application in self-biased photodetectors.

Investigations on synthesis, characterization and humidity sensing properties of ZnO and ZnO-ZrO2 composite nanoparticles prepared by ultrasonic assisted wet chemical method.

In the present investigations, Zinc oxide (ZnO) and ZnO-ZrO2 composite nanoparticles were synthesized by ultrasonic assisted wet chemical method to investigate their structural, optical and humidity sensing properties. The synthesized nanoparticles were characterized by the techniques like X ray diffraction (XRD), UV-Vis absorption spectroscopy, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). XRD and EDS were employed to confirm the phase formation and phase purity respectively. SEM micrographs showed that morphology of the parent compound ZnO is considerably changed with varying concentration of ZrO2. The optical absorption spectra showed that optical absorption of ZnO decreases with increase in ZrO2 content in the composite. The observed band gap values for ZnO and ZnO-ZrO2 composites were higher as compared to the bulk sample. The humidity sensing performance was substantiated for all the samples and the result of effect of concentration of ZrO2 in ZnO-ZrO2 composites on sensitivity, response and recovery time are discussed in detail.