Epitaxial growth of Cu(In,Ga)Se ₂ on GaAs(110)

Epitaxial Cu(In,Ga)Se ₂ (CIGS) films were grown on (110)-oriented GaAs substrates using a hybrid sputtering and evaporation process. The morphological and structural properties were determined by scanning electron microscopy, atomic force microscopy, x-ray diffraction, and electron backscatter diffraction. Pronounced faceting was observed on the surfaces of the films and Ga diffusion was observed at higher growth temperatures from the substrates into the films. The (220)/(204) surface of CIGS was found to be unstable under the growth conditions. The resulting surface consists entirely of 112 type facets with no observable (220)/(204)-oriented surfaces. The epitaxial temperature for the (220)/(204) layers is considerably lower than that on any other surface tested and is attributed to the reduced diffusion distance required for adatoms to reach growth sites. The surface is proposed to grow by rapid nucleation and gradual growth of Se terminated steps across Se terminated surface terraces. This causes the Se-terminated terraces to be rough and leaves the metal-terminated terraces, on which nucleation is slow, relatively smooth.