M. Nicolescu

Surface topography and optical properties of Ge-Sb(As)-S-Te thin films by atomic-force microscopy and variable angle spectroscopic ellipsometry

Thin films were evaporated from powdered GexSb(As)40−xS50Te10 (x = 10, 20 and 27) glassy materials and their optical properties and surface morphology were studied by spectroscopic ellipsometry, performed in the UV-VIS-NIR range, and AFM imaging. For both kinds of quaternary systems, the optical constants (n and k) values decreased with increasing the Ge content in the films, their values being smaller for the GexAs40−xS50Te10 compositions. All films were transparent (k = 0) above 800 nm. The optical band gap energy increased with the Ge content; its value was larger for the GexAs40−xS50Te10 compositions. The AMF images revealed surfaces which are cracks-free and fully covered with uniformly distributed grains having particular structure depending on the film composition. For all the evaporated films, the average mean square (RMS) roughness did not exceed 5 nm, giving evidence for sufficiently high smoothness.

Influence of the substrate type on the microstructural, optical and electrical properties of sol–gel ITO films

AbstractIndium tin oxide (ITO) is recognized as the best transparent and conductive material [transparent conducting oxide (TCO)] until now and its properties are dependent on the preparation method. In the present work ITO films with In:Sn atomic ratio 9:1 were prepared by a sol–gel route on different substrates (microscope glass slides, microscope glass covered with one layer of SiO2 and Si wafers) for TCO applications. The multilayer ITO films were obtained by successive deposition by the dip-coating method and the films were characterized from the structural, morphological, optical, and electrical points of view using X-ray diffraction, scanning electron microscopy, atomic force microscopy, spectroscopic ellipsometry and by Hall effect measurements, respectively. The results showed that the thickness, optical constants and carrier numbers depend strongly on the type of substrate, number of deposited layers and sol concentration. The optical properties of ITO films are closely related to their electrical properties. The enhancement of the conductivity was possible with the increase of crystallite size (which occurred after thermal treatment) and with the reduction of surface roughness.