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  Lei, C.H.; Rockett, A.A.; Robertson, I.M.; Papathanasiou N.; Siebentritt, S.: Interface reactions and Kirkendall voids in metal organic vapor-phase epitaxy grown Cu(In,Ga)Se₂ thin films on GaAs. Journal of Applied Physics 100 (2006), p. 114915/1-8

10.1063/1.2397282

Abstract:
Cu(In1-xGax)Se2 (CIGS) films were grown on (001) GaAs at 570°C or 500°C by means of metalorganic vapor-phase epitaxy. All films were Cu-rich [Cu/(In+Ga)>1] with pseudomorphic Cu2Se second phases found only on the growth surface. During growth, diffusion of Ga from the substrate and vacancies generated by the formation of CIGS from Cu2Se at the surface occurred. The diffusion processes lead to the formation of Kirkendal voids at the GaAs/CIGS interface. Transmission electron microscopy and nanoprobe energy dispersive spectroscopy were used to analyze these diffusion and void formation processes. The diffusivity of Ga in CIGS was found to be relatively low. This is postulated to be due to a comparatively low concentration of point defects in the epitaxial films. A reaction model explaining the observed profiles and voids is proposed.