Monte Carlo computer simulation of the deposition of CdTe thin films by close-spaced sublimation

Thin film solar cells based on the CdS/CdTe heterojunction, where the CdTe polycrystalline layer is deposited making use of the close-spaced sublimation (CSS) technique have attained a very good level of conversion efficiency in recent times. Despite this apparently consolidated situation the debate on the formation of the CdS/CdTe heterojunction is still open indicating that a certain margin of improvement is still possible. In particular, the conclusion that a CdSxTe1−x alloy is formed at the CdS/CdTe interface due to interdiffusion that takes place during fabrication. The extent of the interdiffusion and the value of x depend on many factors such as deposition temperature, gas pressure and geometrical parameters. The situation is even more complicated because while the deposition is in progress, the ratio between the number of Te and the Cd atoms which are reaching the target is invariably greater than one.