AMORPHOUS-TO-CRYSTALLINE TRANSITION OF SELENIUM THIN-FILMS DEPOSITED ONTO ALUMINUM SUBSTRATES

The crystallization of amorphous selenium (a-Se) films prepared by vacuum deposition at < 10−5torr onto aluminum substrates at 20°C was examined. The amorphous-to-crystalline transition was obtained by annealing the films between 70–85°C. The crystalline structures resulting from annealing at different temperatures have been identified by SEM (Scanning Electron Microscopy). X-ray and TEM (Transmission Electron Microscopy) studies revealed that these crystals were of hexagonal structure. The thicknesses of the deposited a-Se films studied in this work were 6250, 9250 and 18,400 Å. The thicknesses of the films were found to be an important parameter, affecting the growth rates of the crystallites, in correlation with the annealing temperatures and times. Upon annealing, crystallization started at the substrate-film interface and proceeded towards the free surface. The radii, r, of the crystallites were found to increase linearly with the increase in annealing time. The activation energies for crystallization, calculated under the assumption of an Arrhenius-type relationship between crystallite growth rate and annealing temperature, were found to increase with increases in the thickness of the film