Annealing behaviour of optical properties and structure of r.f.-sputtered InSe films

Indium selenide (InSe) films were prepared by the r.f. sputtering technique in a range of thickness from 0.25 to 1.5 μm. The annealing effects on the optical transition and structure were investigated by using optical absorption and X-ray diffractometer measurements. The results of X-ray diffractometer measurements showed that the as-deposited film of 0.25 μm thickness at a substrate temperature TS of 80°C has an amorphous structure, while for thicknesses over 0.55 μm the as-deposited films (190°C < TS < 280°C) small crystallites have been induced in the amorphous structure. The optical properties of the as-deposited film of 0.25 μm thickness could be understood from the model of amorphous solids proposed by Mott and Davis. All films annealed at 400°C were crystalline and the c axis in the rhombohedral phase was oriented perpendicular to the substrate plane. A comparison with similar investigations of evaporated InSe films was made. The crystalline structure in the sputtered films was found to be the same as those in the flash evaporated films. The optical transition of crystalline films was also dominated by the direct interband transition, the same as that of InSe single crystal.