Growth regimes of CdTe deposited by close-spaced sublimation for application in thin film solar cells

We have systematically investigated the growth of CdTe thin films by Close Spaced Sublimation (CSS). Thin films of CdTe were deposited onto CdS substrates held at temperatures in the range 250 to 550 degrees C. The effect of substrate temperature and evaporation rate on structure and surface morphology of CdTe films were investigated. Up to 450 degrees C substrate temperature the growth rate was almost constant and decreased exponentially for higher temperatures. The structures of the CdTe films were determined by XPD and a strong (I 11) orientation was observed within the temperature range 250 degrees C-470 degrees C. Above 470 degrees C the texture changed to mostly (311) and (220) orientations. Surface morphology and grain size of CdTe growth was determined with AFM and SEM. The morphology of the layers showed three major modes: Columnar grains with a diameter of 0.2 mu m and a length of 6 mu m for temperatures from 250 degrees C to 350 degrees C, pyrarnidal grains with a diameter of 0.5-1.5 mu m up to 470 degrees C and irregular shaped grains with a diameter of 5-10 pm for temperatures up to 550 degrees C. The roughness increased linearly from 15 nm to 220 nm within the substrate temperature range. (C) 2007 Elsevier B.V. All fights reserved.