Nucleation and early stage growth of CdTe thin films deposited by close space sublimation

Abstract

The early stage growth mechanisms of sublimation-grown thin-film polycrystalline CdTe are evaluated by growth interrupts and ex-situ AFM for growth under 100 torr of inert gas. Development of island size, density and coverage demonstrates that growth proceeds via the process of 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. Application of the nucleation model to influence the growth of solar cell quality CdTe layers is demonstrated by the use of elevated gas pressures to increase grain size. The enhanced grain size is attributed to a reduction in nucleation density arising from a decrease in surface concentration of the deposited species.