Nonuniform strain gradients in CdS/GaAs films measured by reflection high-energy electron diffraction and Raman spectroscopy: A microscopic approach

Strain relaxation at the lattice mismatched CdS/GaAs (100) interface has been investigated by reflection high-energy electron diffraction (RHEED) and Raman scattering. In-situ RHEED measurements indicate a gradual relief of the mismatch strain once the critical film thickness is exceeded. After-growth Raman measurements reveal that the strain profile measured by RHEED remains "frozen" in the grown layer except very close to the CdS/GaAs interface, where further relaxation takes place. A microscopic calculation shows that the presence of nonuniform strain leads to phonon confinement effects, as localized modes appear in regions of similar strains.