Optical studies of carriers’ vertical transport in the alternately-strained ZnS$_{0.4}$Se$_{0.6}$/CdSe superlattice

We present the results of theoretical modelling and experimental optical studies of the alternatively-strained CdSe/ZnS$_y$Se$_{1-y}$ ($y$ = 0.4) superlattice (SL) with effective band-gap $E_g^{\mathrm{eff}}\sim$ 2.580 eV and a thickness of $\sim$ 300 nm, which was grown by molecular-beam epitaxy on a GaAs substrate. The thicknesses and composition of the layers of the superlattice are determined on the basis of the SL minibands parameters calculated implying both full lattice matching of the SL as a whole to a GaAs substrate and high efficiency of photoexcited carriers transport along the growth axis. Photoluminescence studies of the transport properties of the structure (including a superlattice with one enlarged quantum well) show that the characteristic time of the diffusion of charge carriers at 300 K is shorter than the times defined by recombination processes. Such superlattices seem to be promising for the formation of a wide-gap photoactive region in a multijunction solar cell, which includes both III–V and II–VI compounds.