OPTICAL PROPERTIES OF STANNOUS OXIDE THIN FILMS S. S. FOUAD, A. Y. MOURSY, I. EL-FALLAL*), M. A. HARITH**) Department of Physics, Faculty of Education, Ain Shams university, Cairo, Egypt Received 28 August 1991 Thin films of stannous oxide (SnO) have been prepared by the electron-beam evaporation method. Film properties, such as refractive index n, extinction index k, and absorption coefficient oL~ were studied in the wavelength range between 200 nm and 2 000 nm with different methods. The surface roughness of SnO thin films has been found to depend linearly on the film thickness in the range 400 <~ d <~ 2 000 am. The optical transition in SnO thin films shows direct transition corresponding to an optical gap of 2.85 eV. 1. Introduction Studies on stannous oxide thin films have attained new significance because of their increasing use in photovoltalc devices [1], so there has been an interest in techniques and characterization of the prepared samples. Lack in the measured values of the optical constants of SnO led to the need for more accurate experimental data of such important material. The drastic influence of inhomogeneities in thin films on their optical constants, demonstrated earlier [2, 3], has urged the necessity of studying the surface roughness of the prepared films. In the present work the shape of the absorption edge of SnO thin films has been studied by measuring the film thickness, since this can lead to useful information concerning the energy band structure. The shape is of the form expected for direct transition. In addition, we have studied the surface roughness of the prepared thin films as a function of the film thickness. 2. Experimental procedure Stannous oxide SnO powder of purity 99.999 % was used for preparing high quality compact stannous oxide thin films by electron beam bombardment heating in vacuum. The quartz substrates were degreased using hot distilled ~vater or isopropyl alcohol. The evaporation process was carried out in a coating unit under vacuum better than 2 x 10 -5 Torr (Balzers vacuum plant type PAE-121). Generally, the electron source is heated sufficiently by a low tension transformer to evaporate high melting point materials. The rate of deposition was about 3 nm/s. A rotating substrate holder was used to ensure uniform coating. The prepared films were *)Military Technical College, Cairo, Egypt **)Department of Physics, Faculty of Science, Cairo University, Egypt Czechoslovak Journal of Physics, Vol. 42 (lgg2), No. 2 235