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.

We show the existence of a stress-induced coupling between upper-conduction-band states and valence-band states in bulk zinc-blende semiconductors and in their strained-layer low-dimensional systems. This coupling is calculated by an empirical tight-binding method which exactly includes the full crystal symmetry of the strained semiconductor compounds. As an application, we report a study of CdTe-ZnTe superlattices having thin ZnTe layers which exhibit an anomalously high energy for the electron to light-hole transition. We show that the large shift of this transition is well accounted for via mixing between valence and upper-conduction bands.

We compare the binding energy of interacting electron and hole pairs in double quantum wells with and without internal piezo-electric fields. We show that the exciton binding is less sensitive to the piezo electric field than the oscillator strength. This allows many body-effects and bandgap renormalization to be easily produced in strained-layer quantum wells with internal built-in piezo-electric fields, under photo excitation. Our observation was made at low temperature by comparing the behaviour of Ga0.92In0.08As-GaAs strained layer single and double quantum wells grown along the (001) and (111) directions when the densities of photo-injected carriers are tuned over several decades. Comparison between experimental data and the results of a Hartree calculation including the space charge effects reveals that manybody interactions are efficiently photo-induced in the (Ill)-grown samples. Moreover, tunnelling of the two first excited heavy-hole levels can be stimulated for moderate carrier densities making such structure promissive for realising self electrooptic effect device (SEED) modulators.

We have performed a self consistent calculation for both the heavy-hole and light-hole excitons in (Ga, In)As-GaAs quantum wells. The self-consistent light-hole wave function has been found to peak either in the alloy layer or in the GaAs layer, depending both on the indium content and thickness of the (Ga, In)As layer. We have calculated the average light-hole and electron positions and have found that both type I and type II excitons can be obtained from a type II band to band profile with a marginal light-hole potential in agreement with spin orientation measurements.

Thin films of high-quality ZnS were grown on (001) GaAs and (111) Si substrates by metal-organic chemical-vapor deposition. 2-K reflectivity was used to analyze various samples grown at different temperatures. The spectra show two structures at 3.801 eV corresponding to the free exciton and at 3.871 eV corresponding to the E0+Δ0 transition. Theoretical reflectivity spectra were calculated using the spatial dispersion model with two oscillators. Thus, the transverse energies, the longitudinal transversal splitting, the oscillator strengths, and the damping parameters were determined for both the free exciton and the split-off exciton of ZnS. Photoluminescence measurements were also carried out using an excimer laser (308 nm). Both light-hole and heavy-hole excitons were observed, which allow for the determination of the strain that exists in the layer. This strain is due only to the difference between the thermal-expansion coefficients of the GaAs substrate and the ZnS epilayer, and was demonstrated to be a tensile strain. This paper also presents results on the band-gap energy variation as a function of the temperature and photoluminescence spectra when the excitation was varied from weak to very high densities (15 MW/cm2).

ZnSe and ZnTe single-crystal layers have been grown onto {100} GaAs substrates by low- pressure metalorganic vapor-phase epitaxy (LP-MOVPE) using the triethylamine-dimethylzinc adduct [DMZn(NEt3)] as the zinc precursor. The selenium and tellurium precursors were H2Se (5% in H-2) and di-isopropyltellurium (DiPTe), respectively. These two semiconductors have been grown with different VI/II molar ratios, at different growth temperatures, and with an overall growth pressure ranging from 40 to 400 Torr. Optimal growth parameters have been determined by optical means for the two materials. This information was then used to grow ZnTe/ZnSe strained-layer superlattices. We have studied structures grown on both ZnSe and ZnTe relaxed buffer layers which display a drastic dependence of the Stokes shift between photoluminescence and the optical bandgap on the nature of the buffer layer. Growth interruptions have been used to optimize the optical properties of the superlattices. Theoretical modeling of superlattice band structures has been performed using results of optical and structural characterizations. Observations of zone center transitions as well as excitons associated with the miniband dispersion of the superlattices are reported, in agreement with the theoretical calculation.