Piezo- and photomodulated reflectivity spectra of ZnSe/GaAs and CdTe/InSb epilayers

A lattice-mismatched ZnSe epilayer on a GaAs substrate and a near-lattice-matched CdTe epilayer on an InSb substrate grown by molecular-beam epitaxy (MBE) reveal sharp excitonic signatures in their piezo- and photomodulated reflectivity spectra. In the ZnSe/GaAs coherently grown thin epilayer (pseudomorphic film), the contraction parallel to the substrate surface is clearly revealed by the splitting of the valence-band maximum, as seen in the excitonic signatures. The deformation potential constants determined from the splittings and the shifts with respect to the stress-free bulk crystal are in excellent agreement with the bulk values. The MBE-grown CdTe epilayer in the CdTe/InSb heterostructure shows an exceptionally sharp excitonic signature close to that of the bulk.