Type-II CdS-ZnSe strained layer superlattice (SLS) grown on a CdS buffer on (111)A GaAs provide evidence for the intrinsic Stark effect at visible wavelengths. Shifts in photoluminescence (PL) peak energies are expected when photoexcited carriers screen the internally generated piezoelectric fields. Characteristic PL blue shifts under increasing excitation for CdS-ZnSe samples are observed. Transmission electron micrographs show that a superlattice, grown at 400°C, is mostly hexagonal in structure but a similar sample, grown at 300°C, adopts a cubic habit. However, both samples show similar shift factors, 70 meV per decade of excitation intensity, in the range of power densities from 50 mW cm-2 to 20 kW cm-2. These shift factors are only slightly smaller than that found in CdS-CdSe hexagonal superlattices of similar period. This result is not expected since the bulk piezoelectric coefficients of cubic ZnSe are thought to be much smaller than those for wurtzite phase II-VI semiconductors. A resolution of these apparent contradictions may be found by involving the recently reported nonlinearity of cubic piezoelectric coefficients as a function of strain by Andre et al. [Phys. Rev. B 53 (1996) 6951].
- Stark effect
- strained layer superlattice