Study of the Al-grading effect in the crystallisation of chalcopyrite CuIn_(1-x)Al_xSe_2 thin films

摘要

Chalcopyrite CuIn_(1-x)Al_xSe_2 (CIAS) thin films with an atomic ratio of Al/(In + Al) = 0.4 were grown by a two-stage process onto soda-lime glass substrates. The selenisation was carried out at different temperatures, ranging from 400 ℃ to 550 ℃, for metallic precursors layers evaporated with two different sequences. The first sequence, C1, was evaporated with the Al as the last layer, while in the second one, C2, the In was the last evaporated element. The optical, structural and morphological characterisations led to the conclusion that the precursors sequence determines the crystallisation pathway, resulting in C1 the best option due to the homogeneity of the depth distribution of the elements. The influence of the selenisation temperature was also studied, finding 540 ℃ as the optimum one, since it allows to achieve the highest band gap value for the C1 seauence and for the given composition.