Relaxation Processes in Erbium Monosulfide Thin Films

Thin crystalline ErS films have been grown by flash evaporation in vacuum using a pre-synthesized bulk material on quartz and sapphire substrate. The bulk material was synthesized by direct synthesis in sealed quartz ampoules at a temperature of 800 K. During the film growth process, the vacuum in the deposition chamber was maintained at 6 10  Pa, evaporator temperature was  2750 K and the substrate temperature  900 K. Film thickness was about 0.4-0.6 µm. All prepared films had a stoichiometric composition and a NaCl crystal lattice with a lattice parameter a = 5.48 Å. After deposition of films and cooling to room temperature the dependence of electrical resistivity on time was investigated by the four-probe method at atmospheric pressure. It is shown that the relaxation process on films deposited on a quartz substrate proceeds much more slowly than on films prepared on a sapphire substrate. A possible mechanism for such a difference is given.