Interface reactions and Kirkendall voids in metal organic vapor phase epitaxy grown Cu In,Ga Se2 thin films on GaAs

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 gt;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 propose

Comprehensive Comparison of Various Techniques for the Analysis of Elemental Distributions in Thin Films

The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 μm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limit