Molecular beam epitaxy of ZnSSe/CdSe short-period superlattices for III–V/II–VI multijunction solar cells

Results on the molecular-beam epitaxy growth of short-period alternately-strained ZnS$_x$Se$_{1-x}$/CdSe superlattices which are pseudomorphic to GaAs (001) substrates and possess effective band-gap values within the range of $E_g\approx$ 2.5–2.7 eV are presented. Oscillations of the specular-spot intensity in reflection high-energy electron diffraction are used for in situ control of the superlattice parameters. A method to determine the SL parameters (compositions and thicknesses of the constituent layers) based on combined analysis of the grown structures by low-temperature photoluminescence and X-ray diffractometry is developed. It is found that the parameters of the grown ZnS$_x$Se$_{1-x}$/CdSe superlattices are close to their design values and the density of extended defects in the structures is low even though the structure thickness ($\sim$ 300 nm) considerably exceeds the critical thickness for bulk II–VI layers with the same lattice-constant mismatch.