We have studied the temperature dependence of the photoluminescence of tellurium-doped ZnS-ZnSe superlattices. By comparing the reflectivity and photoluminescence data, we were able to identify both free exciton recombination and self-trapped exciton band energy split by 90 meV. The behaviour of the photoluminescence with temperature results from trapping versus detrapping effects which are ruled by an activation energy of 80 meV. This behaviour is analysed in the context of a configuration coordinate diagram.

Raman measurements are used to probe the built-in strain due to the large lattice mismatch in two short-period ZnSe-ZnTe superlattices. In the largest period structure, local information on confinement and strain effects in the different layers is deduced from the LO phonon frequencies. An estimate of the in-plane strain gives evidence of a partial relaxation of both layers; in this structure, folded acoustical phonons are clearly observed under resonant conditions. The Raman spectra of the shortest period superlattice are characterized by a unique structure assigned to an unusual propagative mode resulting from the overlap of the optical bands of the two constituents.

Different ZnSe/GaAs epilayers prepared by low-pressure metal organic vapour-phase epitaxy under the conditions given by Nurmikko and Gunshor (1993 Physica B 185 16) are studied through their low-temperature transmission, reflection and photoluminescence spectra. Several samples are etched out from their GaAs substrate and the properties of as-grown surfaces and etched surfaces are compared. The etched samples seem to be free of in-plane strain and to behave like bulk ZnSe. The free-exciton excited state (n = 2) is clearly observed in transmission, reflection and luminescence spectra. We also studied the thermal quenching of the photoluminescence in order to confirm the origin of some bound-exciton centres.

We present a detailed study of the optical properties of short-period ZnS-ZnSe strained-layer superlattices. These superlattices have been grown by metalorganic vapor-phase epitaxy. We show that the photoluminescence exhibits a low-energy tail due to localization of the exciton to interfacial potential fluctuations. A detailed analysis of the electronic structure has been performed using the envelope-function approach to obtain the valence-band and conduction-band envelope functions and band lineups. This was completed by a self-consistent calculation of the exciton binding energies. In this calculation the marginal conduction-band offset deduced from the standard envelope-function calculation is corrected by the electrostatic deformation produced by the presence of a localized hole wave function.

We have grown ZnSe/ZnS superlattices using low pressure MOVPE. The superlattices were grown onto a relaxed ZnSe buffer and were constituted of 45 periods. The well and barrier thicknesses were chosen from the calculation of critical thicknesses for coherent and free standing situations. Following this analysis we have grown samples with individual ZnSe, ZnS thicknesses of 3 to 9 monolayers. The optical properties of the samples were studied using photoluminescence, photoreflectance and reflectivity experiments. The results of the photoluminescence and photoreflectance experiments are consistent with a free standing model of the strain state, and a typical sketch of potential profile, describing the band structure of such superlattices is proposed. The photoluminescence linewidth is analyzed in terms of interface roughness. The asymmetry of the photoluminescence peaks is modelled using a density of state with a low energy exponential tail, due to the competition between radiative recombination and non-radiative recombination mechanisms. In some samples of lower crystalline quality, bound excitons were observed in the near band edge photoluminescence, which we attribute to impurity interdiffusion, which is favoured by crystalline defects.

We have grown high-purity ZnS layers by metal organic vapour-phase epitaxy onto (100) GaAs and (111) Si substrates using triethylamine dimethylzinc. As is usually reported, the morphology and the crystalline quality assessed by the optical Nomarski microscope and by double x-ray diffraction are similar on both substrates. However, we demonstrate for the first time, using reflectivity experiments along with a theoretical fit, that the crystalline quality of the sample deposited onto Si substrates is much poorer. This observation is interpreted in terms of antiphase defects related to the lack of polarity of the Si substrate.

The optical properties of ZnTe epilayers grown by low-pressure metal organic vapour phase epitaxy on GaAs and GaSb substrates are studied. The layers are grown by using the halide-free triethylamine dimethylzinc adduct and di-isopropyl telluride as zinc and tellurium precursors, respectively. A detailed analysis of the residual strain is offered as a function of layer thickness and substrate nature via reflectivity measurements performed at pumped liquid helium temperature. This is completed by an extensive analysis of near-band-edge photoluminescence spectra in order to discriminate the contribution of residual impurities. Using these precursors ZnTe layers with extremely low contamination rates are obtained.