Thermally evaporated thallium bromide films fabricated at varied substrate temperatures

Thallium bromide (TlBr) is a promising semiconductor material for application in room temperature radiation detectors. In this study, the growth of thermally evaporated TlBr films was studied as a function of deposition temperature, from room temperature up to 200 °C. The growth mechanisms were investigated using scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and optical UV–Vis transmittance. The deposition rate drops from 5to 0.8 μm/min, for increasing deposition temperature. Two growth processes were observed and discussed: one where a columnar-like regime dominates and the other where a smaller aspect ratio is obtained with a larger growth in the horizontal direction. This leads to the formation of micrometer-sized crystalline cubes. The variation between growth regimes is temperature dependent. A reduction of the concentration of bromine, discussed based on the vapor pressure values, seems to influence the final structure and optical gap of the samples.