Evidence of Cationic Antiphase Disorder in Epitaxial Cu(In,Ga)S₂ Grown on GaP/Si(001)

We present a transmission electron microscopy study of epitaxial Cu(In,Ga)S-2 (CIGS) films co-evaporated on GaP/Si(001), in either Cu-rich or Cu-poor conditions. We first unveil the spatial distribution and the orientation of the different phases by means of electron diffraction. From atomically resolved imaging of the CIGS film's atomic structure, we conclude that different chalcopyrite domains, sharing cation antiphase symmetries of the cation sublattice, coexist in the films. We conceptualize at least three types of cation antiphase boundaries (CAPBs), which does or does not lead to a violation of the octet rule, depending on the propagation direction. Even though we observe that epitaxial CIGS is highly prone to cation antiphase disorder, we find that the growth of CIGS in Cu-rich conditions leads to a lower density of CAPBs, as compared to Cu-poor growth conditions. This opens the question of the influence of CAPBs on CIGS electronic properties.