Molecular-beam epitaxial growth and characterization of ZnS-Zn _xCd_1-xS strained-layer superlattices

ZnS-Zn_xCd_1-xS (x=0.56) superlattices with the same barrier (ZnS) thickness (47 Å) and varied well (Zn _xCd_1-xS) thicknesses (23-80 Å) were grown by molecular-beam epitaxy. Reflection high-energy electron diffraction patterns during the growth showed streaks, and superlattice structure was confirmed by the presence of satellites in the x-ray diffraction profile. Low-temperature photoluminescence (PL) peaks from near-band-edge emission shift to lower energy as the well thickness increases, suggesting that the emission is related to confinement in the wells. The full width at half maximum of PL lines increased with the increase in well thickness. A Raman spectrum from a single alloy layer showed two peaks (ZnS- and CdS-like) which also appeared clearly in superlattice spectra. The positions of these two superlattice peaks shift from the single alloy value to higher energy as the well thickness decreases.