The structure and morphology of (112)-oriented Cu(In,Ga)Se2 epitaxial films

The properties of the {112} surfaces of Cu(In,Ga)Se2 (CIGS) are important to the performance of photovoltaic devices based on these materials. Epitaxial CIGS films were grown on GaAs (111)A (cation-terminated) and B (anion-terminated) substrates and the structure and morphology of the films were studied. There are a large number of rotational twins in films grown on (111)B substrates, but not for (111)A substrates. The film surfaces consist of shallow triangular pyramids bounded by one type of ⟨110⟩ step. The steps show both sharp inside and outside corners. New layers nucleated as islands at step edges. The step heights are a mixture of single and multiple atomic layers. The change in surface chemistry from cation to anion terminated affects the measured electronic states comprising the valence band and is probably accompanied by a shift in the valence band edge. There is a distinct difference in step edge shape that shows a difference in step kink density but the expected high kink energy on both surfaces indicates that this may be due to kinetic rather than thermodynamic effects.