Effect of Deposited Pressure on the CdTe Thin Films by Closed Space Sublimation Method

A home-made CSS system in which the CdTe source was above the substrate was used to deposit CdTe thin film. The pressure (3.7~260 Pa) was controlled by nitrogen. The experimental results showed that the deposited rate increased with the decreasing pressure. As the pressure decreased, the center of the film was thicker than that in the edge. Accordingly, the micromorphology obtained by SEM showed that the crystal grain size became larger while the orientation was more random with the decreasing deposition pressure analyzed by XRD. The Non-stoichimometric composition shift of CdTe thin films was characterized by EDX and the Cd/ Te atomic ratio was 0.87± 0.04, 0.88±0.08 and 0.93 ±0.13 as the increasing pressure in our experiments. The calculated results showed that Te-5p orbitals of CdTe with Cd vacancy increased comparing with the bulk CdTe at G-point.