Early stage growth mechanisms of CdTe thin films deposited by close space sublimation for solar cells

The early stage growth mechanisms of sublimation-grown thin-film polycrystalline CdTe are evaluated by growth interrupts and ex-situ SEM/AFM analysis for growth under 100 Torr of inert gas. Development of island size, density and coverage demonstrates that growth proceeds by island nucleation, island growth and density increase, followed by coalescence, channel formation and secondary nucleation. Addition of material to the islands occurs partly by the ‘step-flow’ mechanism. Grains in the completed films are considered to arise from individual nuclei. Nucleation and coalescence models are used to explain the correlation between increased substrate temperature and increased CdTe grain size in sublimation deposited CdTe films.