Influence of deposition temperature, solvent, and solute concentration on the deposition mechanisms and final structure of mercury iodide fabricated using the spray pyrolysis technique

Abstract

Mercury iodide (HgI2) samples were deposited by spray pyrolysis under varying fabrication parameters. Different solvents (water and ethanol) and substrate temperatures (from 40 up to 130°C) were used. Yellowish films were obtained using water and temperatures above 100°C, while reddish films were obtained using ethanol and temperatures below 75°C. The structure and the stoichiometry of the samples were investigated using x-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The yellowish films show lattice constants of 4.379, 7.1953, and 12.5505Å that correspond to a space group similar to the structure of the orthorhombic β-HgI2. The reddish films show lattice constant averages of 4.3550 and 12.2200Å that correspond to a space group similar to the structure of the tetragonal α-HgI2. We observed problems related to the stoichiometry of the films caused by the volatile characteristic of iodine atoms. Typical thickness can be estimated to be around a few microns. The deposition mechanisms and final structure of the samples are discussed as a function of deposition temperature, type of solvent, and solute concentration. Optimized deposition conditions are presented for the development of thin films for radiation detectors.