Growth and characterization of CuInSe₂ epitaxial films for device applications

CuInSe₂ (CIS) epitaxial layers have been grown on both GaAs (001) and In_0.29Ga_0.71As pseudo lattice-matched substrates by molecular beam epitaxy, and characterized for device applications. Despite a large lattice mismatch of Δa/a approximately 2.2%, epitaxial growth of CuInSe₂ has been demonstrated on GaAs (001) showing their film properties strongly dependent on the Cu/In ratio. In-rich films had a large number of twins on {112} planes, and were found to be heavily compensated. On the other hand, Cu-rich films showed distinct photoluminescence emissions indicating significantly higher film quality in comparison with In-rich films. Two dimensional reciprocal x-ray intensity area mapping and cross-sectional transmission electron microscopy showed the formation of an interfacial layer in the vicinity of the CuInSe₂GaAs interface resulting from the strain-induced interdiffusion between CuInSe₂ and GaAs. Reduction in lattice mismatch to Δa/a approximately 0.2% by using In_0.29Ga_0.71As pseudo lattice-matched substrates made possible the growth of high quality CuInSe₂ with predominant free exciton emissions in their photoluminescence spectra and with residual defect densities of as low as p approximately 1×10¹⁷ cm^-3 implying the growth of device quality CulnSe₂ epitaxial films.