Characterization of SnO2 Films Prepared Using Tin Tetrachlorid

We have investigated the effect of deposition conditions of SnO2 films, deposited by chemical vapor deposition using tin tetrachloride and tetramethyltin precursors, on the film properties. The type of precursor and the deposition temperature affect the morphology of the films. The structure of the films is determined by the deposition temperature: films deposited at low temperatures show a mixed SnO and SnO2 phase. The processing temperature and type of substrate determine the impurity content in the films. Electrical properties (e.g. the carrier mobility) and optical properties of the films are affected by the structure and the impurity content in these layers. INTRODUCTION SnO2 film doped with fluorine is one of the most commonly used transparent conducting oxides because of its ease of fabrication, low cost, and adequate performance. These films are usually deposited by chemical vapor deposition (CVD). For laboratory use, a tetramethyltin (TMT) precursor is used with oxygen, whereas industry uses a tin tetrachloride (SnCl4) precursor in the presence of water vapor. In solar cells, SnO2 is used as a front contact, because it allows most of the solar spectrum through because of its high bandgap. The properties of the films must be tailored to the particular type of device. In the case of amorphous silicon solar cells, SnO2 films with a high degree of surface texture are necessary to enhance the device performance through light trapping. In the case of CdS/CdTe solar cells, SnO2 films with minimum roughness are essential to allow the thinnest CdS layers for optimal device performance (1). The deposition conditions must be adjusted to optimize the properties of SnO2 films for each type of application. To obtain smoother SnO2 films, growth temperature must be reduced, which, in turn, affects other properties of the films.