Thermodynamic evaluation of the CdTe deposition by an elemental co-evaporation method under isothermal transport conditions

Abstract

Thermodynamic potential diagrams were used to predict the conditions for depositing cadmium telluride thin films from two independent elemental sources, Cd and Te, while keeping sources and substrate at the same temperature. The potential diagrams also allowed the evaluation of the influence of gaseous contaminants, such as oxygen, on the formed condensed phases. The method may be applied to the deposition of other compounds as long as their vapor pressures are much smaller than the vapor pressures of the constituent elements. The thermodynamic calculation suggested that the film may be deposited under total pressure of 10–4 mbar and at temperatures as low as 450 °C. This total pressure is easily achieved by a mechanical pump and the low temperature range allows the use of low cost glass substrates. The preliminary results showed that the films deposited under the conditions predicted by the thermodynamic calculations were uniform and crystalline, as confirmed by scanning electron microscopy and X-ray diffraction.