Atomic-scale Phenomena During Growth of Cu(In,Ga)Se_2

Growth experiments of Cu(In,Ga)Se₂ (CIGS) on GaAs substrates of various orientations show that the films spontaneously facet to (112)A and (112)B planes during growth, even when beginning from an average non-polar (110) surface orientation. When both the A and B surfaces are present, growth occurs primarily on the B facets and the A facets are relatively smooth. The surfaces of the CIGS/GaAs(111) films of both polarities are covered by shallow triangular pyramids. One type of very straight [102] step dominates the surface morphology. Growth twins are observed for B surfaces but not on A surfaces. The films grow through multilayer island growth and coalescence. The slow growth rate at certain high coordination sites and difficulties in islands coalescence suggests that the surface defects strongly modulate the growth processes. Angle resolved X-ray photoelectron spectroscopy indicate that the first one or two layers of the CIGS (112)B surface are Cu-depleted. We propose that the polar 112 surfaces reconstruct by changing their cation stoichiometry, leading to this change.