Thickness Effect on the Electronic Transitions of SnO2 Films

Abstract

The authors investigated the effect of thickness on the optical properties of thin films of tin dioxide (SnO2) fabricated by the chemical spray pyrolysis technique on glass substrates. Optical measurements were studied in the wavelength ranges 300-900 nm. The optical energy gap decreased from 3.7 to 3.5 eV as the film thickness increases from 250 to 350 nm.Keywords: Transparent conducting oxide (TCO), Optical energy gap, chemical Spray pyrolysis, SnO2.Introduction Transparent conductive films of tin dioxide SnO2 have a variety of applications in optoelectronic devices such as optical filters, solar cells, high stability resistors, display devices, photovoltaic devices, and switches, owing to their specific combined electrical, optical and chemical properties has dominated the present scientific world of thin films and gas sensing[1-6]. Among the TCOs films, tin dioxide seems to be the most appropriate material for different applications, which is chemically inert, mechanically hard and heat-resistant. In addition, they exhibit low electrical resistivity and high optical transmittance. Furthermore, tin dioxide films are more stable than the other TCOs films such as zinc oxide (ZnO) [7–9]. Moreover, they have a lower material cost. Currently, a large number of techniques are used to prepare tin dioxide films. These include chemical vapor deposition [10,11], canon-ray evaporation [12], sol–gel coating [13], laser pulse evaporation [14,15], magnetron sputtering [16-20], electron beam evaporation [21,22] and spray pyrolysis [23-25]. Among these methods, the spraying technique is a simple, economic and commonly used method and it is well suited for the preparation of tin dioxide thin films because of its simple and inexpensive experimental arrangement, ease of adding various doping materials, reproducibility, high growth rate and mass production capability for uniform large area coatings [26,27].