Strain-induced changes in the electronic valence-band structure of a cubic CdS(100) film

High-resolution angle-resolved synchrotron-radiation photoemission spectroscopy was used to determine valence-band splittings and energy-dispersion changes in a strained, cubic CdS film grown by molecular-beam epitaxy on GaAs(100). Reflection high-energy electron-diffraction patterns indicate that the biaxial in-plane surface strain is initially compressively strained by {ε}{~}3.1%. With increasing film thickness the overlayer starts to relax, leveling off at {ε}{~}1.0% for a 170-{}-thick film. From photoemission spectra taken along the normal to the (100) surface, we measured the strain-induced splitting and modification of the energy dispersion of the CdS electronic valence bands along the {Γ}X direction. A comparison of the experimentally determined valence-band structure of the strained CdS film is made with a calculation based on the empirical pseudopotential method. The experiment verifies our theoretical prediction that strain shifts the more strongly dispersive splitoff band by {Δ}E{~}0.34 eV to higher binding energy, away from the upper valence band.